there is an article on this site that outlines how to setup a QT.
generally, you will want a bare bottom tank, a basic hang on filter, a heater, a thermometer, and some PVC
pipe fittings to provide hiding spots for your livestock. lighting is not required but if you have it, use it.
remember to QT your fish for several weeks to ensure they are healthy and disease free. i usually go for 4 weeks, however, i have heard that even that may be too short.
oh, and the size of your QT is going to be based on the livestock you keep. i have all small fish at the moment, so i use a 10 gallon tank for my QT. however, if you are keeping larger species, you may want to have a 29 gallon or even a 55 gallon for a QT... it all depends on your unique situation.