I'm about to render my animation, my first 3D animation.
I need all the frames to render which is 600 frames at 30 fps. So i've turned on "activate time segment" 0 to 600.
Underneath it says range and set by default "0 to 100" should i change this to 600? What is range?
Depends on which one has it's Radio Button "On" as that is the selection of frames which will be used (rendered). The others are irrelevent and can be ignored, so if your timeline is 600 and your main Trackbar (below the viewports) shows from 0 to 600 then the "Active Time Segment" option will suffice (especially if it too says 0 to 600). The other options allow for a different range to that in the timeline, or even for multiple ranges or multiple single frames.
Range simply means consecutive frames starting with a specific frame number and ending with a another specific frame number. In your example you could activate Range and set frames from 0 to 600 - that would produce identical results to setting Active Time Segment (which is also 0 to 600).