the easiest way to do that is to look at the spells section of this side. there are enough diffrent versions of "save/load systems" try it it will be work. or another way which is also simple, if u have the wc3 editor unlimited, is to look at the tutorials maps there are an save/load system too on a easy way with the advanced triggers. but it lags in the variables u need all of the advanced variables so if u have made your map it would be bad to use the advance triggers if u dont want to make more than 100 new variables So my tip: search in the spells section!
My tips: 1) Search at F.A.Q. 2) If you wanna singleplay save\load use cache,else use integer 3) What you want to save? -Items -units -Levels _________________________________
And if u cant decide what save/load system you want, see the comments of what other people have posted about them. Reading the pros and cons is also a good way to decide what your looking for. Good luck.. and if u need help on changing the save/load trigger, post it, ill reply for sure if i see it.