OVER HEATING PROBLEM WITH 1998 PLYMOUTH NEON?

i got a 98 neon it over heated and was losing water all at once and no viewable leaks but somebody has to told me it was head gasket my first question is how do you know if it is gasket? and second is does any body know if Bars Leak 3-Step Head Gasket Repair Kit is any good or not? cause we cant afford to get new head gasket right now and was also told to check oil for foam but the oil is good nothing but oil. THANK YOU