I’m planning to buy a guitar amplifier then I’m going to record a guitar instrumental. My problem is, (i don’t know what are their names, but what I’m saying is like Line out, Line in, Headphones, Auxiliary stuff like that) I don’t know what amplifier will I buy because some has Line Out, headphones, others don’t have. I just want to be sure. Thanks. 
Are you on Windows with a laptop? Which one?
You understand that an amplified guitar sounds very different through a microphone and the amplifier/speaker cabinet than it does with a straight electronic connection. Many people find that the electronic transfer is sterile and flat compared to the acoustic capture. The speakers and cabinet are a major part of the sound of many instruments.
Acoustic capture is a nightmare because you get the room, too. If you record in your mum’s kitchen, it’s going to sound like it.
So we need to go there before we go equipment shopping.
Koz
See this excellent article from Sound-on-Sound: http://www.soundonsound.com/sos/Dec02/articles/recordingguitars.asp
this is cheaper than an amp+mic etc … http://www.behringer.com/EN/Products/UCG102.aspx