Writing about common grammatical errors, including those with which you struggle, is an interesting assignment. Run-on sentences and comma splices are a challenge for many writers. In fact, many online sources cite these as ranking among the top ten mistakes people make in writing. According to Grammerly.com,

when a writer joins two independent sentences with a comma instead of separating them with a period or a coordinating conjunction, that's a comma splice.

In other words, a comma does not replace a period or conjunction when joining two related thoughts together. For example, being hungry and eating are related concepts. People generally eat when they are hungry. However, it would be incorrect to write,

I was hungry, I ate.

These two separate thoughts are not joined together properly. Instead, a writer could use a period or a conjunction to link the two thoughts, as in the following example:

Example 1: I was hungry, so I ate.

Another way of presenting the same thoughts would be,

Example 2: I was hungry. I ate.

The latter might not be particularly elegant, but it is correct grammatically.