98 ford ranger, hoses that hook to heater core.?

my step son changed the heater core, that wasnt bad. the hose connections at the plastic fittings leak, and the dealer gave him new o rings to install. but something is hoaky, there are two in one hose and three in the other. he is in pensicola right now for training and i need to get it fixed for his wife. should there just be one o ring in each hose? i am going to buy the new end connectors, and was wondering if i have to use a special tool to snap them together, or if they just push on really hard? im just a old hose clamp man, so i need help with the new stuff. thanks for the help.