Crating

  I can remember the days (decades ago) when crating was considered 'mean'.  Some people felt it was like putting their dog into a prison.  This was the same time period when some people had no problem with shoving their puppy's face in an poo accident, hitting their dog while screaming 'NO' and then throwing the dog outside.  It didn't matter that they were gone for hours and failed to take the dog out to potty prior to leaving.  If the puppy chewed a shoe up, it was the same treatment.  Thank goodness times have changed!
  Dogs are descendants of the wolf (or so we are told), and all wild dogs have dens.  Dogs are very comfortable in a den and crates are in-house dens.   Dogs don't think of them as jail, as they don't understand our penal system. Pugs usually love their crates and feel very safe in them.  It's more than a potty training issue...it's about your pugs safety.  I use wire crates as the puppies like seeing me move about the house, and they don't feel isolated (like people who shut a dog in the bathroom.) 
When I get a folding wire crate home, the first thing I do is zip-tie the upper corners and remove the lid.  I'm not crawling in the crate to get my puppy while it backs up into the back end.  It's so much easier to just reach in from the top...to change water and newspapers etc.  Sometimes I'll use two crates pushed up against each other (both doors open) and zip-tie the doors to the side of the opposite crate so no one can get out through the little gap.  If I do that, I use bedding to cover the hump in between crates so no one gets their feet stuck.  I had one family (that adopted a puppy from me) get a crate/play area from Walmart online. It is not only beautiful but expands out:

http://www.walmart.com/ip/Richell-94164-Expandable-Dog-Crate-Small-Autumn-Matte/28928362

  I do have my crate rules though.  If a puppy is crying, I never approach the crate until that behavior stops.  I have food and water available at all times, bedding on one side (with toys) and newspaper on the other side.  Sometimes people have to be gone (working) longer than a puppy can 'hold it', so it's unfair that they be sectioned off in a small area and forced to urinate in their bedding....and then sit in it all day.  Crying in the crate is usually a puppy that feels a bit lonely.  Wait until the behavior stops or you will be trained to 'come' when the puppy demands it.  Not good!  As soon as the puppy changes behavior to being quiet, go get him and take him outside for potty.  I never speak to a puppy in a crate as they need to know it's for quiet time.  You can never have company come over and have a quiet puppy in the crate if you interact with him every time you walk by.  I take the puppy outside and say 'go potty' in a serious tone.  Once the puppy potties, I change my tone to one of great happiness while praising him.  They have no idea what you are saying..but will know what the tones mean (after a while)...and then words later.  I then pick my puppy up and go back inside for play time on the floor.  Never leave your puppy unsupervised!  Their little back teeth are coming in when real little and any cords seem like fun to chew on.  You can have leather raw-hides to chew on, but these have to be supervised also.  Chewing on them makes them mushy and the puppy can choke on pieces.  I like the antlers and cow hooves myself.  They seem indestructible.

Once our puppy play time is over, I put the puppy back in the crate.  I use a crate that is at least 32 inches long.  When your pug is older, he may want to go in there for nap time...so buy one big enough to start with.  When your puppy is on the floor playing and has an accident, clean it up with vinegar...and don't say anything to the puppy.  They learn quicker with positive reinforcement (outside when they do pee), and can't hold it very long as little babies.