Do you need a guarantee company to apply for studying abroad from the school?

Of course.

This is no problem.

To study abroad, you can apply directly to the school, and you can apply for a study visa if you get the admission from the school.

If it is a job, you need to get a work contract from a foreign company and get a company guarantee before you can apply for a work visa.

Specific situation, specific analysis, depends on which country to go to!

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.