i attempted to make my sig last night and it came out alright imo..
i do understand clipping masks well though so i can help you with those. the one use that i know is to put a picture into a shape ex: fit a picture of someone into a heart without the excess outside the heart.
i don't really know any terminology or whatever so bare with me c:
what you need to do is open a new file and put in the photo you want to use. usually i just drag and drop from my downloads (i have a mac so this may not be the same for you) typically you need to press enter when you put in a new image to save it.
this layer should be called 'background' or something else. next, you are going to duplicate the layer. do this by right clicking the layer and selecting 'duplicate layer'. another layer should appear with the same name as the previous, except with copy afterwards.. ex: 'background copy'.
next, you are going to select the shape tool in your toolbox. it is below the cursor tool i believe. (if you right click, it gives you a few shapes to choose from but you probably want custom. choose the splat icon) when you click it, the top bar should change to the shape option. on the far right of this bar should be 'Shape:' then a random shape. you can select whatever shape you choose. if you click on the little arrow, more will come up. in that option box there should be a setting icon to the right. click that and at the bottom of the selection there should be another list of shape groups. if you click one, it will ask you something about changing the current shapes blah blah blah, click OK.
after you find the shape you want, create it on top of your image (do this on your copy layer). a new layer should appear called 'shape'. move this underneath your copy layer. then right click your copy layer and choose to create a clipping mask. once that is done, make your 'background' layer invisible by clicking the little eye next to it.
there you go!!
i have no idea if any of that made sense, but hopefully it helped. i may have missed a step so i'm going to test it out really quick to make sure.