Yes, you can use most i/o pins as Digital Inputs or Digital Outputs in any combination.
You do not specify the chip you are using, but some i/o ports default to Analogue mode and must be Set to Digital mode before the Tris instruction.
The datasheet I/O Ports section details which i/o ports have an Analogue function.
IF your using a PIC Microcontroller have a look at the ADC section of the Data sheet. For PICs the Special function register to look at is: ADCON1. This regiser selects the pins as analogue or digital.