Began is the simple past tense form of begin, which means to start.

It all began one day about ten years ago.
Begun is the past participle form of begin.

We can’t stop this process once it has begun.
Now, let’s look at the specific ways to use these conjugations of begin, as well as how to avoid common mistakes.

Using Began in a Sentence
When to use began: Began is the simple past tense form of begin. It means to commence or to start.

For example,

You’re late! Dinner began at 7 o’clock and it is now almost 8:30!
The snow began falling early in the evening last night and had accumulated to over two feet by early this morning.
There are several idioms and expressions that use the word begin. A couple of these, which are listed below, can also occur in the simple past:

I’m pretty sure it would be began