I have a rubbermaid glue-gun. I'd like to know how to insert a new glue stick. I tried and it doesn't seem to 'click-in' properly.

I do not believe there is a manual. there are instructions on the package. Insert the glue stick and turn on the gun. When the glue melts and the trigger moves glue will come out the front tip. This model has 2 temperatures so if it delivers too fast or runny you can lower the temperature. You pull the trigger to push the glue stick into the heating element to melt the glue. It is pretty straight forward. As the glue stick is consumed you stick in another glue stick. I suggest testing on something before using on your project. Do be careful of the hot end. It will definitely burn you if you touch it and the glue coming out is nearly as hot as the metal.

Is the light on? The problem may be electrical, you can try plugging it into a different outlet. Try one that you are sure is working (ie unplug something that is already working and try the glue gun there). If it is getting power, there must be a problem with the interior heating coil, in which case you will have to unscrew the casing and replace some parts

you get what you pay for, i hope you can learn to use it well!

i would let the glue set for at least a few hours before inserting the screw. use an industrial strength (contractors) glue stick

Insert the glue stick into the back of the gun. After doing this plug in the gun and allow it to heat up. When the gun reaches the correct heat level you will be able to pull the trigger of the gun which will pull the stick into the gun. This will only happen if the gun is hot enough.

with some glue guns the sitting with a stick in them wile hot the stick will get hot enough to where the gripper that advances the glue slips try to bush it through some to where you can add a new stick in or when sitting for longer periods unplug to allow to cool then re heat when needed.
hope this helps

No need for concern. Just leave it there and then the next time you use it push a new one in as needed.
I haven't met a glue gun yet where you can take out the last remnants of glue stick.
If you prefer to remove it try this:
take a paper clip and straighten it (any thin,metal object will work) Heat the glue gun,unplug it,and then heat the end of the paper clip with a lighter/candle.
Insert it into the end that you load from,sticking it into the glue stick. Wait a short time and then pull the paper clip out. The glue stick should come out with it.
I find it easier to leave the glue stick in as I said,but it's your choice.

I would try J B Weld.can find at auto parts store or hardware store.

Gather the materials needed and place them on a flat surface near an electrical outlet. Examine the glue gun. Locate the metal rest. This is usually attached to the barrel of the gun and is shaped like a "W." Make sure it folds out and locks into place. Locate the trigger. This is just behind the barrel on the underneath side of the gun. It should be a solid piece of plastic shaped like a slice of pie. Just above the trigger, is the barrel loader. This is where the glue sticks go into the gun. Inside the barrel loader there is a smaller round piece of plastic. This is what actually pushes the glue stick through the barrel. Pull the trigger and watch the piece of plastic move with it. Pick up the electrical cord and examine it. Make sure the prongs are secure and not bent. Make sure the cord has no breaks in the outer lining and there are no frays at the base of the gun where the cord attaches. Plug the glue gun into the electrical outlet. Allow the gun to heat at least 15 minutes so it reaches operating temperature. When the gun has heated at least 15 minutes, insert a glue stick as far as it will go without forcing it. Now pull the trigger until a small drop of hot glue forms on the tip of the gun. Practice gluing on the paper plate. Pull the trigger until a ball of glue forms on the plate. Release the trigger and quickly press the tip of the gun down onto the surface of the plate and pull it to the side. This will break the glue and stop it from stringing out when you pull it away. Continue practicing until you get the right amount of glue you want for the object you imagine using. When you pull the gun away, there may be a small string but this will break off easily. When you have the perfect amount of glue and only a tiny string forming when you pull away, you are ready for your project.