Cars can be costly to run and repair and so any jobs that you can do yourself will help keep repair costs to a minimum. You do not have to be a trained mechanic to work on vehicles but many modern cars are so overly complicated that it can be hard to do so without a good sound knowledge. Some more simpler jobs may be able to be accomplished by watching video tutorials but you should only attempt to do so if you are confident you are able to finish the job as intended and safely.
One job that many people do themselves is to fit new brake pads and discs. This is often straightforward as long as the callipers are easy to remove.
When buying the new parts, you need to make sure the fitment is the same. Ideally you want to remove the old ones and double check the part you are ordering is correct. If this is not possible then you should make sure that you can return the part for a refund or exchange if it isn’t the right one.
Try and avoid doing jobs on a car when you are on your own, especially if you are going to have to be going under the vehicle whilst it is jacked up.