So I have a 50 mL volumetric flask filled all the way to 50 ml. The 50 ml included 2.182g of .150 M cobalt nitrate. I than use 5 test tubes. The first test tube I fill with 1ml of nitrate and 4 ml of water, the second I fill with 2 ml nitrate and 3 ml water, the third with 3 ml nitrate and 2 ml water, the fourth with 4 ml nitrate and 1 ml water, and fifth with 5 ml nitrate and 0 ml of water. So each test has 5 ml in total. Knowing this information how do I find the concentration of each test tube. I was told I would need to use the formula m1v1=m2v2 but I don't know how. Help please.

m1 is the initial molarity.
v1 in the initial volume.
m2 is the final molarity.
v2 is the final volume.

What you need to find in each case is the molarity.

For the first test tube, you have 4 mL of cobalt nitrate and 1 mL of water.
What is the molarity of the 4 mL of cobalt nitrate? This is m1
What is the initial volume of cobalt nitrate? This is v1
What is the final volume of cobalt nitrate? This is v2

Put those in your equation and you'll be able to find m2.

Same procedure for the others.