Which courses I need to work in the IT field? I know the basics of networking.

depends on your previous filed of studies and interest, networking then go for cloud and voip and securities..

As Sajid said, it will mostly depend on your interests and taste.

For networking you could begin with CCNA of CompTIA Network+ (this last one is brand independent)

A very useful one is MSCA from Microsoft

If you will get into virtualization VCP from VMware)

And it's always useful to be ITIL Foundaiton certified (best practices to offer IT as a service)

There are many other flavors to certify... security related, PMP, branded, unbranded, Linux... etc.

Hope it helps in the first steps of your professional career.