Theory:

Grammar 1 - Simple, Continuous and Stative Verbs

A CONTINUOUS action is something that has duration, that lasts for some time.
For example, sleeping for 1 hour is a continuos activity.

Breaking a window, or opening the door is not a continuous activity, but a SIMPLE activity, because you just do it and giving such an activity a duration is illogical.
For example, it doesn't make sense to say I was opening the door for 1 hour. You just say, "I opened the door."

So the difference between simple and continuous actions is clear.

There is a third group of actions which are continuous, as before, but different. They are called STATIVE.
For example, I love my wife makes sense, and it is a continuous activity, but I am loving my wife for 10 years doesn't make sense.

The information given above directly influences the way the verb ends.
Verbs in the simple form do not end in ING, but all verbs in the continuous form end in ING, except for stative verbs.
For example, I am sleepING now, I was sleepING when..., I will be sleepING ....

All continuous verbs also need to have the verb TO BE.
For example, I AM sleepING now, I WAS sleepING when... and I will BE sleepING when...

I PLAY tennis is the PRESENT SIMPLE, while I AM PLAYING tennis now is the PRESENT CONTINUOUS.
I PLAYED tennis yesterday is the PAST SIMPLE, while I WAS PLAYING tennis when ...is the PAST CONTINUOUS.
I WILL PLAY tomorrow is the FUTURE SIMPLE, while I will BE PLAYING when... is the FUTURE CONTINUOUS.