I have already downloaded MiKTeX and TeXStudio and I would like to know how to run them.
As per TeXnician comment above you need to have installed in the best order. If you installed TeXstudio first its best to re-install it, after you update MiKTeX. For guidance with
MiKTeX installation (including system-wide distribution) see current user manual & FAQs NOTE the installation manual STRONGLY advises a single user install (To be clear. If you are a super user just install as 1 user, if you have 2 or more users then chose if its easier for 2 single users to update, rather than having to update 3 or more times (once as administrator plus yourself as user plus all the other system-wide users.)
If you are trying to install in a portable fashion, I recommend you do a standard install first to check how it works, then for portable installation guidance see configuring portable texstudio-to-use-miktex portable
For help with
TeXstudio installation (in English only) see user manual
When you start-up TeXstudio it recognise the installed MiKTeX and make some alterations to work with it. Once TeXstudio is running you can usually use the menu Help > User Manual (in my case I can not since its blocked by browser security settings) so I use the user manual link above.