Hello, welcome to res! :) It can be a bit confusing at first but you'll soon get the hang of it!
Many players use Stocks as a means of income. They can be found under Games > Skill > Stock Market. At the bottom of this post I'll put an explanation of how to play stocks :)
Apart from stocks, a good way for beginners to earn tu is through hatching and selling pets. Alternatively you can sell your hatches for 100k-150k each. You can also earn tu by hunting some of the rarer eggs and selling them on the egg market~ The species hatchable in achromatic for the month are usually in extra high demand so keep an eye out for those! This month's achros can be found on a recent update (just click the rescreatu logo at the top)
I hope you enjoy yourself here! If you need any more help don't be afraid to ask, it's what we're here for ^-^ Feel free to rmail me if you're more comfortable with that. Otherwise just post on this thread and I'll get a notification~
Stocks
Basically you want to buy stocks when the Share Value is below 50 and sell when it's above 350 (or 400 if you're prepared to wait a bit longer). However not all stocks are worth buying. The first seven on the list plus FAS, HOL, SQU, STA, THE and TOY are some good ones. Observe the stock market over a while, take note of which stocks go high frequently and invest in them when they go low again.
Stocks refresh every 12 hours, so at midnight (reset) and noon res time. However you can only buy/sell a total of 50,000 shares every 24 hours (this refreshes at midnight/reset). If possible, try to buy/sell the maximum 50,000 shares in the 24 hour period unless nothing is high or low enough to be worthwhile (this doesn't necessarily apply to beginners, but rather once you have some tu to your name).
Stocks are probably the easiest and most reliable way of making tu. Many of Res's users earn their fortune purely through stocks. On a good day you can earn 30mil profit or more just from stocks! :)