A press fit means an interference exists between the hole and the object in the hole. The pin (or whatever it is) is slightly larger than the hole it is going into. The amount of interrference will depend on a few things, the most important factors being the nominal diameter of the pin and hole and the degree of press fit that you want.
The assembly of a press fit will involve either heating of the hole to enlarge it or cooling of the pin to shrink it prior to assembly. Some people will simply jam the pin in, but that's usually not the way to go.
To diassemble may be a tougher issue. It is usually very difficult to heat only the hole and not the pin to facilitate enlargment of the hole. You can try it, but depending on how much material is around the pin and if the pin and hole are different materials, you may not have any luck doing that. If it is simply something pressed on to a shaft then you should have good luck in that case. If it is a pin pressed into a hole, you may have to consider having the pin drilled out.
All are good ideas for your problem. A press fit is generally 0.0005" per 1" of diameter. On small diameters an arbor press,a jacking bolt with a strong back, or a bearing puller will work great. For larger diameter problems you'll probably need to heat the outer part (whatever it may be) quickly and jack the center piece out. Depending on your enviroment and the tools you have available. Always remember to clean both part very well prior to disassembly.
Heat the hole or use dry ice to shrink the shaft. Press fit is when you have interference between hole and shaft. Let say that the hole dia is between .5002" and .4999", the shaft dia. would then be between .5003" and .5006". after fitting the shaft in the hole, you would have compressive stress between the two items.
