Different microcontrollers can communicate?
Any microcontroller can communicate with another microcontroller in many different ways. 

There are various standard communications protocols for which most micros have at least one or more dedicated peripherals built in such as UART, SPI, I2C, USB, CAN, etc.

For micro to micro the most common is usually SPI, I2C or UART, of which your micro has all three. You need to read up on each to become familiar with the pros and cons (speeds, number of pins taken, complexity, etc) but the datasheet will have all the necessary info, and there are hundreds of tutorials out there (and related questions on here) to help you.
Frequency wise, as mentioned, you can choose to set the speed to whatever is within spec for the peripheral.

Even if you don't have the hardware peripherals built in you can "bit bang" simple communications such as UART or SPI. So the short answer is yes, there is always a way.