I really need to know so i know what to buy

A guitar amplifier (amp) is the electronic device used to take the signal that a guitar produces and amplify the signal to a much louder level so that it can then be ran to a speaker where the sound is reproduced much louder. The pickup on a guitar takes the mechanical motion of the string and converts it to a very weak electronic signal which is then sent to the input of the guitar amp. The amp takes this weak signal an proceeds to magnify that signal considerably and in the process adds aspects of tonal properties to it (equalization, etc.) it then sends this amplified signal to a loud speaker which converts it back into mechanical energy which we hear as sound. A combo amp has the amplifier and speaker all in one package. A head is an amplifier by itself without a speaker. It requires a speaker cabinet for operation. A speaker cabinet is a box with speakers in it (no amp)
A combo amp is the best bet for most playing because it has the versatility of having both an amp and a speaker in one package. These can range from very small practice amps to larger amps with 2 speakers and enough wattage to play at a loud volume. A separate amp head and speaker cabinet combination is usually used for very high volume situations.