where do i start when i log into the game?

You start by planting your colony somewhere. Follow the tutorial on how.

If you meant what location you should start. Well that depends. There are basically two types of locations. 1) the crowded and 2) the desolate.

1) The crowded will have a lot of players in an area. This will give you the most to conquer and to be conquered yourself. It's not a good idea to start in these locations if you coming in half-way through the round. (unless you don't care to be conquered). If you are conquered, just sit back, relax, and build structures and units. Perhaps later you can liberate from your conquerer by rebelling.

2) These location have fewer players than the crowded. So less to conquer but also less to conquer you. Which will give you somewhat a better chance. I say somewhat because you might still get conquered if you coming in late in the round.