A fragment is an incomplete sentence.

Fragments occur when the subject or the main verb in a sentence is missing OR when the sentence begins with a word that forces it to be dependent on another sentence to complete its meaning (dependent clause).

In the morning. (fragment)

When combined with an independent clause (I will make breakfast), this fragment can become a dependent clause and, in turn, create a complete sentence:

In the morning, I will make breakfast.

Try turning these fragments into dependent clauses by pairing the with independent clauses...don't forget to separate them with commas if the dependent clause comes first, but not if it comes 2nd.

Under the table, the children were playing.

The children were playing under the table.

Running late.

In my opinion.

Without hesitation.

On the other hand.

In the meantime.

At the top of the mountain.

After the storm.