"I play the guitar."
Translation:Ich spiele Gitarre.
(die) Gitarre is a typical guitar.
(der) Bass or (die) Bassgitarre is a bass.
(die) E-Gitarre is an electric guitar. You could also use (die) elektrische Gitarre, which is literally 'electric guitar'.
There quite some terms for guitars with 5 strings. I found "(die) fünfsaitige Gitarre" (literally '5-stringy guitar'), "(die) Fünf-Saiten-Gitarre" (literally 'guitar with 5 strings', but as a compound word) or "(der) 5-Saiter".