You can find just about any tool you need and their uses at http://www.parktool.com/ you can also find multiple how too's here , depending where you are, other brands like Cyclus, Var etc are available. For what's changed in the last 20 years, is many things, with out knowing what you have currently, for road bikes, headset size, BB standards, rear wheel OLD, discs brakes and caliper mounts to start with.

You don't say how old / what you bike is, but if it's from the late 80's / 90's, it could have many parts which although updated versions are now in use, the older versions still use the same tools currently available.