too many questions. almost all of which have answer in the forums already, you just need to search for them.
when people talk about buying now while the market is crashing, we mean only to buy companies we know are sound and will survive. you still have to research your own options and make a decision to where you will put your money.
companies don’t always go up, many go sideways or even down, you need to know what kind of stock you are getting involved with and what you can reasonably come to expect. these are not things anyone else can tell you, you have to do the work yourself.
to learn about the features of Trading 212, please refer to the numerous video tutorials on their youtube channel, that will cover everything you are expected to know at the minimum in regards to how the market works and how the T212 platform will serve you in your goals.
also @tariq please remove your email from public display.