How Do I Potty Train My Rat Terrier Puppy That Is 4 Months Old And Has Had No Prior Training?

Is your terrier an indoor animal?  Or does he stay outside?  In the case of an indoor dog there are these pads that you can set on the floor and each time that you terrier starts to urinate move him over to the pad.  If you continue to do this he or she will eventually learn that when it needs to relieve itself the pad is where it should go.  If you keep your dog inside but want it to relieve itself outside when it starts to go in the house take it outside.  if you repeat this over and over again it will expect to be let out when it has to go.

Placing pads or newspaper on the floor doubles the work you have to do - first the puppy learns to use the pads/paper then you have to re-teach him to go outside.
Place sheets on the floor to protect the floor by all means but start training the puppy immediately to go outside.
First, you have to learn when your puppy wants to go - that's first thing in the morning, every time during the day when he wakes and immediately after eating. So be ready and and get him outside before he pees or poos - then tell him what you want him to do - you can say any word you want - cabbages if want - but always the same word and have a sense of urgency in your voice.
Every time his peeing coincides with you saying your word - praise him like it's the 4th of July. same goes for pooing - he'll soon get the hang of doing it when you say - and bingo he's trained -

Get A Crate!!! We have been raising Terriers for over 38 years and that is the first thing we tell everybody. You need a crate that your puppy can comfortably stretch out in and stand in. You do not want it to big or they may potty in it.

Next you need to get a schedule. Puppies at 4 months need to be fed twice per day. After feeding the puppy must go to his designated potty place. Do not play with your puppy at this time. You should plan on spending upto 15 min. trying to get him to go when you first start. Once your puppy goes be sure to make a big deal about what a good puppy they are and give them a treat. Always use the same word when trying to get them to go. The puppy should have nothing to eat or drink at least two hours before bed. They are going to need to out as soon as you get up, after naps and after hard play or eating. When your puppy is not in the same room with you they are in their crate. Do not give them the run of the house. At four months they should be able to go upto 8 hours overnight without having to out, but if they fuss during the night get up and take them out. Do not make this play time. It is in and out for potty only and then right back to bed.
The main points are Crate, Schedule and Consistency.

I give my dog people food in her bowl but she does not eat it in less you life it on the plate

If its still not potty trained call the vet