Start familiarizing yourself with things like threading standards (BB, headset etc), shell width, rear spacing, brake type and reach, stack height, chainline etc.These are concepts you need to understand to pick components that not only fit your frame, but are compatible with one another.
Tools will be needed. Knowing what you have existing and what you plan to install will often determine what specialty tools you require.
Certain tools that will never be wrong are cone wrenches and allen wrenches.
Some places to find good information.
https://web.archive.org/web/20191117...TE_Welcome.htm
https://www.parktool.com/blog/repair-help
https://www.sheldonbrown.com/