First things first, you need to search up "How to get Minecraft on PC". It will come up with a video. Scroll down until you reach "Buy for PC and Mac | Minecraft", from minecraft.net. Click on the link and it will take you to a screen saying "CREATE YOUR MOJANG ACCOUNT", and boxes to put in your email adress, date of birth, and password. I would not advise using a child's account. Use an adult one. Once you have done that, click the "CREATE ACCOUNT" button at the bottom of the screen. It will take you to a page asking you to enter your verification code. Go to your gmail and an email from Mojang will appear and it will have your verication code. Go back to the page to enter your code in. It will then take you to a page telling you to sign in again. Do that. If you have signed in as a child's account you will be required to put in your parent or guardian's email adress in. Follow the instructions in your parent's email to get Minecraft. If you are using an adult's account then you will be taken to the screen where you buy it.Choose a name and then choose your payment method, buy it and then wait for it to download.
Here is a link to the Mojang sign in site
When it is finished downloading go onto the Minecraft Launcher and it will say DOWNLOAD. Download it and after the download is finished you can press play. To play on servers click multiplayer, then add servers. You will then have to add in some server names and the ip. adresses. One example is Cubecraft, and the ip. adress is cubecraft.net