Inking and Line Art is when you go over your initial sketches/drawings with darker and cleaner lines. It is one of the final steps to finishing up the page and giving your comic a completed look. Given the digital age, the more common phrase these days will be referring to Line Art.
For brushes, I personally use Kyle T Webster’s brushes for inking (which you can find directly in Adobe Creative Suite), but feel free to explore other brush packs or create your own! You can find brush packs that are compatible with whatever drawing program you are using. And the good news is that most of them are downloadable for free.
Keep in mind, there is more than one way to line art. Find what works for your particular style and look at other artists for what they do with their line art.
Line Art Example
Here is an example from my comic of how I clean up my sketches with line art. You can see adjustments and other details added between the two.
Module 6 Ex 1:
From the previous exercise in module 5, apply your line art. Save this exercise for when we get to the color module.