Always focus on the Icons that are present everywhere in the software. For an example on the ribbon and on the dialogue boxes of tools etc. They are self-explanatory and give you information about how a tool will function. So watch every icon very carefully.
For an example watch the dialogue box of the Mate Constraint too. To activate this tool just go to the Assembly tab>Position panel and click Constrain tool to activate it. Now the Place Constraint dialogue box will open. The mate constraint is active and default solution type selected is mate. Focus on the solution section and see what the icon shows. Watch the image below.
This Icon clearly states that mate constraint will work on entities that are in opposition to one another.