Question

how to represent any vector 3d space...

Answer 1

vector is represented by an arrow .
Head of the arrow indictes Direction of the quantity which you are representing and the length of arrow indicates it's magnitude.

Answer 2

By the general unit vectors that are...  I cap , J cap , & K cap So we can write ant vector as...  V = xî +y jcap + z kcap  It can be represented generally and positionally in a 3d space along x,y & z axes respectively.