When applying to a school in Russia, should I start applying for an invitation letter after submitting the application form? I hope someone who knows can tell me the details, thank you very much!

First of all, you must understand that the invitation letter is issued by the school you are applying for. After you fill out the application form and the school approves it (you still need someone to ask for this), it will need your various document information and send it to the Immigration Bureau to process an invitation letter for you. The Immigration Bureau usually takes about a month to process the invitation letter. After the invitation letter is completed, it will be sent to you in China (if the school helps) or you can ask a local person to pick it up for you.

After getting the invitation letter, you can go to the Russian Embassy in China to apply for a visa abroad (of course, various other procedures are required).