In the first video they talked about RGB and CMYK. CMYK stands for cyan, magenta, yellow, and black they are mostly fore commercial print. RGB is red green black for web or screen, things that are not going out for print. The difference between a fill and a stroke is that the fill is the area inside a path, and a stroke is the "outline" what surrounds the fill. You can have multiple strokes. Paths are were your artwork travels is a straight line between to points called anchor points. Anything you create in illustrator is a path a "skeleton". Anchor points are joints that hold paths together without them paths don't have a point to start or stop. when you click on an anchor point with the direct selection tool they become active. You can create 2 types of paths open and closed paths. The closed paths are the basic shapes such as square circle etc...and the open paths are the ones which have nothing connecting it the fills are a little weird. To take two separate paths and join them together joint points really close then use the direct selection tool  then object> path> joint or CMD+J. If in-points aren't match up join is not the right thing to do, so you average. You can split paths with scissors tool  that splits paths based on anchor points selected, you can also use the knife tool but is not as precise, after cutting go to isolation mode and move.  With option or alt tool knife is more precise.