How to write data from another site to a Bitrix site?

Question

1C-Bitrix

Hello everyone) The task is to add from the site, say test.ru, an entry to the site test_bitrix.ru.
What is the best way to do this?
I read that an attempt to stupidly get into the Mysql database, and score records there, will end in failure. If not immediately, then during the update.
I also read that Bitrix has its own API and they say that everything can be done through it, but I did not find a connection between Bitrix 24 and the site on Bitrix.
I'm trying to google the data exchange algorithm, but all the time I stumble either on actions through the admin panel, or on some other garbage.
Bitrix experts, please answer, what is the easiest way to unload goods from a regular site, using php methods to the Bitrix site, so that it does not lie down? Well, or maybe there are special functions for exporting imports with code.
Security issues are not of great concern, there is no time to delve into the structure and architecture of Bitrix.
You need to transfer only one record, but
1. With pictures
2. Check if there is such a category of the record, if not, create
And other small questions, the answers to which can be useful if I can’t find a solution
How to link a picture to a product in Bitrix? Let's say I still managed to create a record and get an id, what method can I use to attach a picture to it?
And if anyone knows, please advise which sky is a free Bitrix course, but it is for the backender, not the admin.
I would be grateful for any hints

Answer 1

Manually

Answer 2

The most canonical free backend training course - https://dev.1c-bitrix.ru/learning/course/index.php...