The guitar may have made it’s home with the E but the A is most certainly it’s mistress. In blues playing, the A is one of the most common keys to play in. There are probably many reasons for this. It too lends itself to having many open strings to ring out like the E and it also lends itself to lead playing as you work your way up and down the neck of the guitar.
In any case, the A is a very important key for guitar players and it goes without saying that the A7 chord is therefore quite useful as well.
Practice getting your fingers into position. Lift your fingers off and on the guitar in the A7 position and then practice going from A to A7 while strumming. Progress into practicing the A7 along with some of the other chords you have learned.
I would suggest practicing with E, E7, A, A7, B and B7. You’ll be glad you did when you get to the next lesson.