First, simply you have to open google and search the website of unity. The link is https://unity3d.com/get-unity/download .You can copy this link and paste it on Google the website of Unity is now opened. 

Now you have to see on top left corner of the website there will be written "Get Started" and click on it.Then it will open a download box in which there is a paid download but we have to download unity in free so there is an individual group right next to teams group so, click on individual group.There will be two options Student or Personal click on that which you want to use and they will be free.Now come back to the home screen and there will be two options "Unity + download" and other will be "Download Unity Hub" so, you have to click on Download Unity Hub after clicking it it will open a dialog box in which there will be License Agreement and in bottom there will be an button "I agree" click on it and then other dialog box opens in which you have to write where you have to download the unity and then click on install it will also in bottom.Then an other dialog box open so click on finish it will also in bottom.Now you have downloaded the unity hub so open it then go to installs and click on "add" button which is on top left corner of unity hub.Now you have to choose the version you want to choose I prefer use the latest version and then click on next and now new page open in which you have choose which platform for you want to make your game like Android,IOS,Windows etc.Now click on Install and your editor will be installed. Now how to make a project so it is pretty simple just you have go to project and click on the button add now a new page is opened in which you have to choose your game's name and choose that it will be 3D or 2D and then click on create. Now everything is done so make games and earn money.