The vast bulk of plastic model kits are made from polystyrene plastic. The standard cement that is used to "glue" this material is commonly referred to as "polystyrene cement".
In actual fact, "polystyrene cement" is neither a cement nor glue. It is a type of solvent which actually dissolves the polystyrene plastic wherever it is applied. When two pieces of plastic on which one surface has been applied are mated, the dissolving plastic actually melds the two pieces together.
Polystyrene cement comes in a number of forms -
liquid (in a bottle)
Liquid in a dispenser with a needle applicator
The tube version is the one most of us grew up with. It is thick and viscous and can get very "stringy". Tube cement usually ensures a strong bond but can be messy and any wayward blobs of cement can damage parts of the model surface which will need repairing.
Liquid poly cement is better. It is thinner and easier to apply. This is normally done with a brush. Often the brush is attached to the inside of the bottle. Because it is being applied with a brush, it is easier to place the cement accurately and there is less chance of damaging adjoining surfaces.
Dispensers with applicators are a relatively recent innovation and are the best (in my opinion) way of applying polystyrene cement.
Here are some examples of polystyrene cements -
Liquid in a bottle -
Dispenser with applicator -
There are other polystyrene cement manufacturers out there. In the UK, Humbrol is probably the best known - along with Revell.
If you are trying to glue disimilar materials - such as polystyrene plastic to white metal, or white metal to photo-etch, or acetate plastic to polystyrene, that is where other glues need to be used.
These are usually -
cyanocrylate - i.e. "super glue"
white PVA type glues (similar to Evo Stick wood glue)
two part epoxy type glues
Hope all that helps.