I have a CPU with built in graphics, is that okay for playing minecraft and dayz?

That totally depends on the maximum amount of CPU and which kind of graphics card you have inside your pc.

http://www.systemrequirementslab.com/cyri?gameName=minecraft&itemId=11356&p=r
And
http://www.systemrequirementslab.com/cyri/requirements/dayz/11929/?p=r
You can run a test to see if your PC can run games in the drop down search list.

Please follow specs of Mine craft and Dayz.
And check gpu specs with CPUZ software.
You can check and decide if match to play or not

That depends what cpu you have. Built in graphics are called integrated graphics, these can be used for 2d games and some 3d games. Day z requires Dedicated graphics(NVIDIA GeForce GTX 560) of at least 1 gb Video memory. You might not be able to play day z.