Once you know where the notes are that you want to play, you have to get them vibrating.
Most beginners decide to play with a flat pick, or plectrum.
It's the easiest way to get a clear, loud sound out of guitar, especially on steel strings. Nylons aren't as suited to playing with a pick and prefer to be plucked by the fingers. I have always been a finger style player and I never use a pick. I find them difficult to control, but only because I never use them. I tried for a while to use finger-picks, which slip on the ends of the fingers, but they also were uncomfortable for me.