There is a tendency in spoken German to use shorter forms of words. This is something that is especially noticeable in the first person present tense of verbs: ich geh, ich fahr, ich komm, etc. instead of ich gehe, ich fahre, ich komme etc. While the former should not be used in any kind of formal writing and would certainly lose you points on an accredited German test, they are nevertheless considered standard German and not slang or dialect.
This dropping of the letter is called an elision. The basis for dropping the -e above is die Sprachökonomie or "speech economy," a positive description of which is "the improvement of communication through simpler modes of speaking." A less flattering motivation for shortening words might be "simple laziness."
Since the dropping of the -e in first person present tense verbs is standard (though not formally correct) German, the use of an apostrophe to notate the missing -e is not only unnecessary, it is incorrect. According to Duden: Ein solches nicht vorhandenes e wird nicht durch einen Apostroph ersetzt. However, it is Yabla's responsibility to teach formally correct German, and it is a priority to avoid giving the impression that ich komm is formally correct. Therefore, Yabla has decided to let the German learner know that a letter is missing from the formally correct version by using an apostrophe to indicate the missing -e: ich komm'.
Here are some examples of elisions on Yabla German with the missing -e marked with an apostrophe. Because of the apostrophe, you learn that the word is not formally correct and requires the missing letter to be formally correct. Remember, however, that the formally correct German way of writing the elision is actually without the apostrophe!
Nee, ich komm' von [aus] der Pforzheimer Gegend.
No, I come from the area around Pforzheim.
Caption 33, Unterwegs mit Cettina - an der RheinfährePlay Caption
Ich fahr' eigentlich auch total gerne Schlittschuh.
I actually also really like to go ice skating.
Caption 3, Diane - auf dem Weihnachtsmarkt - Part 2Play Caption
Ich geh' bloß, gern nach Italien in Urlaub.
I only, like to go to Italy on vacation.
Caption 32, Fasching - mit Cettina - Part 1Play Caption