That stand pipe on the back should turn a full 360• and that's what will adjust your water level in the skimmer body. Install it and play around with it. Also note that it'll take some time to break in. Some skimmers can take a few days, maybe even a week or two. Others start pulling right away. How deep is the water in your sump? That's going to effect it's overall performance as well. Are there no instructions on it? Have you looked on youtube for a video on that skimmer?
Having put micro bubbles in the sump is normal and part of the break in process. You'll also see this after cleaning the skimmer as well. Have the water in the column of the skimmer so that it's at the bottom of the collection cut.