Main reasons behind adding "first posts" in the review queue are:
Spam, spammers are usually people who create new accounts and then post some spam, so this queue can help in filtering that. Actions: [Flag] it as spam, downvote if you wish as the automated bots do clear things depending on the flags + downvotes.
"Sincere" new users who ask for the fist time, usually they are new to the SE platform and the way we run things here, so the queue can help in putting things in track before they pile up and ruin the whole spirit of SE. I personally think of it as private lessons to these users who didn't bother to read the Help before they ask. Action: [Edit] in case it needs to be reshaped to fit in, or [Flag] it in case it is off-topic, broad, etc.
Please note, you still can add comments, and that's an action, try it, and once you add a comment the review buttons will change and show the [I'm done] button.
Clicking [Skip] is not an action, [Skip] button was meant when you are not sure what to do, so clicking skip will give the chance to someone else to look at it. Always click [I'm done] after doing one of the actions (flag, vote, comment, vote to delete, etc.) or click on [Looks OK] if the post is ok and needs no actions. Clicking skip will not add to your review achievement.
Regarding upvoting, use your normal upvoting criteria. Personally, I would upvote new users when they ask a new question just as a welcoming gesture, as long as the question follows SE standards. I never downvote new users, I prefer giving them the benefit of the doubt.