You can do one of three things:
(a) You can cool the salty water. Ice will form and the ice will not have salt in it. One you pull out the ice and melt it, you will have pure water. This is called freezing.
(b) You can evaporate the water by boiling it. If you collect and cool the vapor, the water you collect will be pure and all the salt will be left behind. This is called distillation.
(c) You can pump the salty water thought something called a reverse-osmosis membrane, which is a kind of special filter. On the side that you pump, the salt will be left behind. On the other side of the membrane you will obtain pure water.

If you distill the water you can get the pure water. Once all the water had evaporated you are left with the sea salts. Distillation means that you heat the water salty solution and collect the vapor and cool it down, to get the water back into the liquid phase

A good way to do this would be to boil the water. When salty water boils only the pure water will turn into steam, but the salt will be left behind.

You could do this with a test tube of sea water. Put a little sea water in the test tube and seal with a stopper, but use a stopper which has a hole in it to connect a length of tubing. You can put the other end of the tubing loosely in another test tube. Now boil the water in the 1st test tube using a bunsen burner. The sea water will boil and turn into steam. Hot steam rises and will rush into the tubing. As the steam moves along the tubing it will cool and turn back into water (condense) This clean condensed water can then be collected in the second test tube.

When all the sea water has boiled away you should notice that the salt is left behind.