1. what is the difference of tone between blues overdrive and distortion because I have both of them

2. what is the effect of a flanger pedal?
If you can't tell the difference between the two you don't need both.

Generally, however, blues tones have much less gain and sound warmer than distortion because overdrive tries to mimic a tube amp driven hard and distortion is generated artificially.
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2. what is the effect of a flanger pedal?

listen to paul gilberts "hurry up"

and i would suggest you buy one with out knowing what it does and what it sounds like in person.
I saw a flanger pedal at best buy and I wondered what it did because I never used one before.

I have a distortion and a blues overdrive.

my friend is getting some money along with warchest and GH3 so I tricked him somehow into getting me a pedal for my guitar lol

as long as I'm not paying for it, I'll use the pedal.
You can Youtube Flanger effects, some examples of it are the intro to Pantera's Cowboys from Hell and Van Halen's Eruption.
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A flanger pedal makes it sound like a jet engine is playing your guitar while revving its engine.

There is a better description in the stickies somewhere in the GG&A forum.