A full response to "how to play minecraft" would take forever. Of the two basic modes, "creative" and "survival", creative is the least stress. Nothing is hostile, you have unlimited access to all resources, no health or food to worry about, breaking blocks is instantaneous, etc. You can even fly around. You can do whatever you like, with the corollary that you kind of have to come up with your own activities since most of the structure of the game is missing. Unless you're the kind that likes to jump right in at the deep end I'd recommend that your first experience be in creative mode, at least until you get the hang of things.
Beyond that, I've been playing for years now so if you have any specific questions feel free to ask. It also helps a lot to be able to find an experienced someone who can play with you online for a few "days".
In "survival" mode you have to build, grow, or find everything for yourself. You have to worry about food and health, and hostile mobs ("mobiles", aka monsters) spawn in the dark places like caves and at night. The first day is therefore kind of important, as you'll want to find a safe place to be before your first nightfall. If you don't then you'll have to be dodging skeletons, zombies, and spiders all night. That can be either fun or traumatizing, depending..
My "first day checklist"...
1.. punch a tree. Literally within 10 seconds, find the nearest tree trunk and start breaking it for wood.
2.. take the logs you get from the tree and make some planks.
3.. make some of the planks into sticks
4.. make a crafting table
5.. place the crafting table down next to you and use it to craft some wooden tools from the sticks and planks. You'll want at least an axe, a pick, and probably a shovel. Use the axe to get more wood. The pick is for (cobble)stone, and the shovel is for dirt.
6.. build a tiny hut. The roof can be open (for the first night), but It should be about 4x4 blocks lengthxwidth, and 2 blocks tall. you can use dirt, planks, stone, sand, or anything else you like. Mine are usually dirt or planks, but anything that's handy where you spawn is fine.
7.. knock a hole in one wall of the hut that is 1 block wide and two blocks tall.
8.. use some planks to craft a door, and put the door in the gap you just made. You might also want to break the crafting table down at this point and place it back down in the hut.
At this point you've got a little protected area that you can hide in during the first night. Don't worry about anything fancy to start. Keep a minimal mindset for the first few days.
If you have time on your first day after doing the above, or the next day if not, then the next things you'll need are light and a bed. Look around for some stone. You'll need to mine 9 blocks to make into a furnace on the crafting table. Put it next to the crafting table.
Put a log or two in the top part of the furnace, and a couple sticks or something wood in the bottom for fuel. pretty much anything can be used as fuel.. doors, wooden tools, sticks, logs, tree saplings, etc. There's an optimal way to do things, but I'm not going to spoil the fun by getting into it here. if you put enough fuel in the bottom part you'll turn the log into charcoal. a stick and coal or charcoal will make a torch. Torches make light. Monsters don't spawn where there's light. Torches are thus handy for making places like caves or the inside of structures you build safe places where monsters don' surprise you.
Beds are kind of like save-game markers. When you die (note that I did not say "if" ) you will respawn either at the world spawn point where you started the game or near the last bed you slept in. You also need to sleep every three days or so in recent minecraft versions. If you don't then if you go outside (exposed to sky above) you will be attacked by phantoms.
To make a bed will take "wool" and wooden planks. Wool you can create from spider silk or from sheep. There is a shear tool, but it requires iron to make, which you'll have to find as iron ore and refine in the furnace. You'll have to kill spiders for the silk, so that's also problematic for newbies. Sheep will also drop their wool when killed, as well as food (which you'll also be needing). Sheep are non-hostile mobs, so killing sheep is probably the best way for a newbie to get wool. Mkae the wool into a bed, and cook the meat in the furnace.
At this point you should be relatively safe. You can make a sword and go off to fight mobs. You can make a hoe and start a farm for growing seeds/wheat, carrots, potatoes, and beetroot. You can build pens and farm pigs, cows, chickens, and sheep. (Cows can be milked, and produce meat and leather when killed. Sheep for wool and meat, like I mentioned. Pigs are just for meat. Chickens produce feathers, which are necessary for arrows, and also meat.) You can make a pick and start mining for iron, gold, emeralds, redstone, and diamonds. You can build a huge castle. Or you can just go off and explore the world.. find villages, avoid raiders and other hostile mobs, etc. There are horses, donkeys, and llamas for pack animals and riding, if you can tame them.
If you get bored with all that there's a portal you can build, which lets you get to the Nether. Mostly lava and nasty mobs, but the Nether also is the only source for key ingredients for potions. There's underwater temples, abandoned mines, the End and the End Dragon and End cities. Lots of stuff to work for.
Here's the minecraft wiki, and like I said, just ask..
For the extreme MC survival players...