I've recently been doing lineart, and illustrations but I've heard that layers could be useful in such artwork in the case. Can anyone explain as simply as possible what these layer modes do like multiply, screen, blend, darken, light. Thanks.

they make the layer partially transparent (the amount depends on the mode formula i guess) and they change the colors of that layer in a certain way, depending on the colors that are beneath the layer.

You can read in detail here http://gimp-savvy.com/BOOK/ in section 5.6 Blending modes, you can find the examples there. That book is for Gimp, a raster application, Inkscape doesn't have all the modes you can see there. The best way to see what they're about is to try it yourself. Make 2 layers with colorful objects, then change the blend for the top one

you can also search for "layer blend modes", you'll find lots of tutorials

the Inkscape Guide has a good explanation specific to Inkscape at http://tavmjong.free.fr/INKSCAPE/MANUAL ... ters-Blend

But as prkos suggested, these blend effects are common to many applications.