Here are examples of the two errors:

comma splice: In the second advertisement we see that the man leans on the woman's body, he is obviously in pain.

run-on sentence: In the second advertisement we see that the man leans on the woman's body he is obviously in pain.

Either problem (comma splice or run-on sentence) can be corrected in five ways.

 1. Use a period. Write two sentences.

In the second advertisement we can see that the man leans on the woman's body. He is obviously in pain.

2. Use a semicolon.

In the second advertisement we can see that the man leans on the woman's body; he is obviously in pain.

3. Use a comma and a coordinating conjunction.

In the second advertisement we can see that the man leans on the woman's body, and he is obviously in pain.

4. Make one of the independent clauses dependent (subordinate). To do this, use a subordinating conjunction such as after, although, because, before, if, since, though, unless, until, when, where, while.

In the second advertisement we can see that the man leans on the woman's body because he is in pain.

5. Reduce one of the independent clauses to a phrase, or even to a single word.

In the second advertisement we can see the man, obviously in pain, leans on the woman's body. 

Run-on sentences and comma splices are especially common in sentences beginning with transitional words or phrases such as the following:

This isn't to say that you should never begin a sentence with any of these words. It only means that you should make certain that if you do begin a sentence with one of these words, the result is neither a run-on sentence nor a comma splice.