For those who need help: Learn how verb conjugation works in German. If you can't find anything online, it may help to make a chart from this data and keep it near you for quick access.
Example verb = Spiel
A good way to remember the sie vs. Sie is either capitalization or conjugation of the verb. If the verb is not conjugated as -t, but rather as -en, then it is the "they" form. If the word "Sie" itself is capital, then it's the polite form of "You (guys)". If it isn't capital, then chances are it will be necessary to check the conjugation of your verb.
But this is really only for regular verbs! Big caution!
Big? How many irregular verbs are there in the present tense?
Besides the obvious sein (which is just completely irregular) and haben (which loses the -b- in a couple of forms).
The rest all pretty much follow the same pattern, with only minor modifications (e.g. vowel change as in geben: du gibst or -e- disappearing after a final -r or -l).