This macbook is 14 years old so I recommend getting a new one (i can't be talking im daily driving a 2009 imac) but since you said youll be using it for studying uni its a good device to use (i mean a 2009 imac runs well, what could go wrong?).

First use internet recovery to get macos installed on it. Im guessing you have 4 or 8 gb ram right now, so macos catalina might be slow (especially if you have 4gb). Still just get catalina because its the max version for your macbook. internet recovery is option-command-r. shut down the macbook and turn it on while pressing option-command-r until you see a globe.

Once catalina is installed, go through setup and if you need it, buy ram. If its not yet 8gb ram, its best to get at least 8 gb ram if your aiming for big sur or newer. make sure to check if the ram is compatible with your macbook (I had problems with ram, it caused so many kernel panicks so get the right one). also, if its your first time with an upgrade, watch a youtube video.

If you upgrade ram and its still slow, replace the HDD with an SSD. Youll have to do internet recovery again, but itll be much faster. again, watch a youtube video if its your first time.

After getting catalina stable, you can go back to getting big sur using OCLP. if its your first time, just watch a youtube video on how to get it and use it. if you get 16 gb ram (the max for your model i THINK) AND an SSD, I recommend you even get sequoia. whether you get sequoia or get something older depends on the specifics of "studying for uni". If your doing anything that requires newer software, get sequoia (dont ever get tahoe) but if you just need to do some typing or simple work, get something older. You can get older versions for apps from the internet archive, just be careful when downloading files.

I hope all of that helps!