Hi there. This means that if you do something (like make a cake, or learn a language, or anything at all!) you should always try your hardest and do the best you can. Otherwise the results won't be good enough, and you will know that you can do better. There are a couple of slight variations you will hear- "Anything worth doing is worth doing well" "If you're going to do something, do it well" Or one that is a kind of joke, a quote from Mick Jagger- "Anything worth doing is worth overdoing!" (So if it is a good thing, then do it LOTS!)

It means if you are going to do something, put all of your effort into completing it, don't give up and most importantly don't take any shortcuts. It implies that if you don't do it right then the end result will be worse than if you hadn't done it. For example: If your goal is to paint a room, you should research the right color, buy professional paint, painter's tape and a brush and apply several layers. If you give up halfway through or use cheap paint or try to take a shortcut by only using one layer of paint then the room will probably look worse with the new paint than it did with the old. Thus "it's worth doing it right otherwise don't do it". I hope this helped!

Do not do something unless you are going to do it well (good). Example: If you are going to run in a race, do not run in the race unless you are well prepared, have practiced and are going to run fast and do well in the race. Otherwise there is no reason to run the race. I am not sure if that was clear. I cannot think of a better example. :D