Find the point on the y axis that is equidistant from the points (2,-1,1) and (0,1,3) and then find a point not on the y axis that is equidistant.

If the point is on the y-axis, that means its coordinates are (0,y,0). So you just need to find the distance from that point to (2,-1,1), as well as to (0,1,3), then set them equal to each other and solve for y.

Do you know how to find the distance between two points?

When it comes to answering the second question, just arbitrarily pick two numbers for any two of the three coordinates, and use a variable for the third one. The just do the same process as before, solving for the variable. For example, you could pick (x,1,-1) or (0,1,z) or any other coordinate you want.