Hey guys got a couple of doubts

Hey so as the title says, I've got some questions. I've been playing City Skylines 2 since last few days after watching couple of videos on YT. Before making this post, I read the FAQs and all but it didn't help me much. My Bad. Anyways here are my questions: - - So i did build a city and population is around 30-33k but now there is no demand. Demand isn't increasing now. What shall i do for that?

• Secondly, till now my city is mostly based on rectangular blocks. I make a main rectangle with one 6 Lane road and smaller 4 Lane road rectangles inside and make buildings inside. Now the problem is that, idk how to make proper buildings. I mean i do know how to build it but it's like sometimes when I click the area suggested where building should be made, it starts building automatically all over the green area but sometimes it doesn't. Why so? And this happens for all kind of buildings like Houses, offices, Commercial and industries.

• Thirdly, there is a lot of clogging in my city for cars. I am making 4 lanes minimum anywhere. I made multiple different paths from the main road itself to go towards different parts of City but it's not working out. What shall I do?

• Fourthly, there are those intersection bridges, how to use them? I tried putting that one inside my city but those lanes are too small for even 4 Lane roads.

These are a few doubts I have and ik they are silly but I am just starting out. Pls help me if you can. Even a YT video suggestion is good. Thank you.