You get a max of 5000 points per single player level. There's something like 158 such levels, I might have miscounted. That's around 790,000 points for completing all the single player stuff. https://www.warzone.com/wiki/Levels
-> this lands you just before level 39.
If you want to level up, then lottery games are your best bet. They often have level requirements though, so you'd need to play a bunch of regular games. RT is fewer points/game than Multiday, but RT also completes much faster. IF you are efficient and skilled, you can do well playing many games at once. For a beginner, it would be best to play fewer RT games and get familiar with the history graph/analysis tools on the lower left.
The problem with single player is that its very slow, but the points are guaranteed.
The problem with multiplayer is that you are required to defeat another human to get the points, and until you start learning a bit, those wins will be tough to get.
The best solution for levelling as a whole, is joining multi-day lottery games and tournaments. (Lotteries are non-strategic games intended to be completed in a single turn). Some of these filter players out based on levels though; the last such group I joined filtered to level 35+ players. Fortunately, you will get bonus points for defeating your first opponent of each account level.
If you end up playing multiplayer, start with autogames. I don't care how boring the elite players find it. Your goal would be to learn the basics, and you don't want the distractions of new maps and templates.
Some players will help you if you need advice - like me - but usually the people who need the help don't ask or don't listen, so eh.