While you can always use your fingers to strum and pick strings, a lot of electric guitar players tend to use plectrums, which is the name for a small triangle of plastic.
You hold it between your thumb and first finger and you can strum and pick the guitar with one. They amplify the strings better and can help with accuracy.
There are many different types of plectrum, but generally they're grouped by thickness. Thin plectrums are softer and better suited for strumming.
Medium thicknesses are good all rounders for both rhythm playing, lead and everything in between.
And thick plectrums are best suited for accurate lead parts because they don't bend so much.
Plectrums come in many different shapes, sizes and thicknesses, not to mention materials. The best thing to do is to try a selection and see which feels best to you. And don't forget to buy more than one - you'd be surprised how many of these things you can lose!