Can you explain the differences between present continuous, simple present, simple past, and past continuous?

See below:

Explanation:

$\left(\begin{matrix}\text{ & ul"Simple" & ul"Continuous" \\ "Present"| & "I study" & "I am studying" \\ " Past"| & "I studied" & "I was studying}\end{matrix}\right)$

Simple vs. Continuous tells us about action. Present tense tells us that something can happen but doesn't mean it is happening. Continuous tells us that something is happening.

Past vs Present tells us about time.

And so:

Present Simple - I study - ex. I study math.

We know that the person speaking at any given time might be studying math, but we don't know if they are right now.

Present Continuous - I am studying - ex. I am studying math.

We know that the person speaking has a math book open and is actively studying math.

Past Simple - I studied - ex. I studied math.

We know that the person speaking at some point in the past studied math. It could have been earlier in the day, last month, or 80 years ago. We just don't know.

Past Continuous - I was studying - ex. I was studying math when the phone rang.

We know the speaker was recently studying math but that something happened to divide up the time (for all we know, the person could still be studying math).