If you talk about a tutorial you should always give a link, if it's a video tutorial give the time position as well.
Your issue seems to be a missing coincident constraint. It is not enough to get somehow through a tuorial, you may have to go back and try to understand the reason why all these constraints are used and how they work. Video tutorials are not always the best choice, you may have a look at the Tutorials
in the wiki. If you have learned the very basics about sketching, then this Sketcher tutorial
may give you more explanations.