Can I put FX pedals in front of?

Should I put a digital multi-fx pedal in front of a tube amp? (Epiphone Electar 10W, specifically) I've only owned solid states and I was told that it isn't wise to throw digital fx (I have a DigitechRP60) in front of tubes. Also, I need info on how to correctly use the amp. I bought it used so there is no manual. There is a gain, volume, middle, b and tremble knob ( I think) How do I obtain overdrive ? All of my solids had the OD on. I don't gig, any info is appreciated!