1) PU is one of the tiers that Showdown uses. Supposedly it means either "Partially Used" or "Poorly Used", though I've never heard a definitive answer.
2) Just looking at your team list, you might wanna add in a Rapid Spinner/Defogger in order to deal with entry hazards. Also....what tier were you planning on using this team in? It would fit comfortably in UU, but Togekiss is BL, which bars it from being used in UU battles (and idk if you wanna use this team in OU or not). We might be able to help you more if you post the full sets that each Pokemon is using.
3) There's a "Look for a battle" button in the top left corner of the screen. Select the tier/format you wanna battle in (OU, UU, Doubles, etc), then select the team that you're going to use, then hit that button. You should be paired up with someone in a few seconds. The rest should be easy to figure out.
If ya got more questions, feel free to ask.
Nah ンン
“No, I... I have to be strong. Everyone expects me to."