I really like my Clover bias tape makers. I can make bias tape very fast with them. My tips for using them are (1) starch the fabric before cutting the bias strips, (2) cut a long, tapering point in the fabric to make getting the tape started easy, and (3) keep the iron close to the tape maker's tip. You can use a pin underneath the tape maker to get the tape started. If I am making long lengths, I sometimes leave the iron in place after I have gotten the tape started, hold the tape maker in place with my left hand, and pull the tape from under the iron with my right hand. I have tried other brands but, in my opinion, the Clover brand is far superior. The directions tell you how wide to cut your strips but, if you forget, simply double the size of the opening and then subtract 1/8" inch to get your strip width.
There are Youtube videos that demonstrate these tape makers. Here is a link to one, not necessarily the best one:
https://www.youtube.com/watch?v=m5KOjp4k7-o