So I'm looking at buying this relay module for a project. 6 of the 8 relays at most will be used at the same time. My question is will I have to use some external power source in order to activate the relays? Or will the arduino's 5 volts be enough? If I need an external power source how would I go about it? Thanks!

Those relays (coils) draw 75-80mA each when active.
An Uno draws about 50mA.
USB power is 500mA max (an Uno has a 500mA polyfuse).
External power for the relay board might be wise (old 5volt cellphone charger).

Is this for your car tail light project?
Then you also need a suitable buck converter.
The 5volt regulator of an Uno can only power one relay when powered by 12volt.

Is this for your car tail light project?

Yeah it is, is a buck converter just like a 12v to 5v step down? So a car charger usb adapter?

Most car buck converters (cigarette lighter types) can deliver more than 500mA.
I see no problem powering that 8-relay module and the Uno from it.

Ok thanks a lot friend!

Why not get a relay module with 12V relays that control the relays with 5V logic? Then you have the relay coil power from the car's 12V system.