A lot of electric and acoustic guitar playing is done using a plectrum. Ever since I first started playing guitar I have always prefered Jim Dunlop plectrums, and I have gone through a lot of plectrums! My favourite plectrum is the Jim Dunlop Standard Ultex
If you're just starting out, then I'd recommend getting a variety pack, where you can try different types and thicknesses to find one that feels good for you. A good one would be the Jim Dunlop Medium/Light Variety Pack (Pack of 12).