A redox reaction is a reaction which involves both a reduction reaction and an oxidation reaction.
Reduction reaction is when a species gains an electron.
Oxidation reaction is when a species loses an electron.
A simple way is to remember -
Oxidation
Is
Loss
Reduction
Is
Gain.
Example - in a galvanic cell between Zinc and Copper (you'll learn this next year)
The following reactinos take place -
Zn -> Zn2+ + 2e- this is an oxidation reaction as Zn has lost electrons.
Cu2+ + 2e- -> Cu reduction as Cu has gained electrons.
The Zn acts as an reducing agent and Cu acts as an oxidating agent (as Zn causes the reduction action to take place and Cu causes the oxidation reaction to take place).
That's all you'll need to know I believe.