Let's look a bit to the future.
The next step (lessons 11 >) is all about past happenings. Which will be a little more complicated. Knowing the verb forms used for future events helps with past tense forms as well. And it is not too difficult, as long as we stay away from complications. (Aren't there always?)
I always κλείω τὴν θύραν
Difficult? No, just insert an S between stem and ending.