arduino mega board voltage of I/O pins and what is the use of 3.3v in that board

Projects General Guidance
1

hii,

I want use mega board in my project with 5V supply. But 3.3V supply on board making confused. Please explain the role of 3.3V in mega board

2

The 3.3volt pin is an auxiliary 3.3volt/150mA power supply output, not used by the Mega itself.

You can use it to power 3.3volt sensors etc.
Leo..