Moulding technologies can reproduce extraordinarily complex topographies. But are equally useful producing everyday shapes too.

Plastics come in two flavors, thermosetting (which means that once formed the plastic cannot be remelted - if re-heated it will char and burn), and thermoplastics which can be remelted. Therefore thermoplastics are much more versatile and useful than thermosetts (which have only niche applications, mainly in heat resistance).

There are a whole range of ways of Moulding plastics

1. Compression Moulding for thermosetts,
2. Reaction Injection Moulding (RIM) of two part reactive products, for Polyurethanes (PU) the reactive process creates the pressure that fills the Mould with plastic.
3. Rotational Moulding where thermoplastic powders are released into the interior of a pre heated Mould that revolves on the end of an articulated arm and the powder sticks to the hot Mould wall. Used for Kayaks, tubs, troughs and large containers, especially custom made items. Rotational Moulding is a fairly primitive process that is great for small runs and small markets.
4. Blow Moulding, where an extruded tube of molten thermoplastic is trapped in a Mould and inflated to fill the Mould. Typical applications range from simple milk bottles to extremely complex automotive fuel tanks.
5. Injection Stretch Blow Moulding, where thermoplastic, in this case PET, carbonated drinks bottle are manufactured by first injection Moulding a test tube shaped preform that is then reheated and inflated to fill the bottle Mould.
6. Injection Moulding, the ubiquitous Moulding format, used for making everything from disposable widgets to critical medical devices. Basically nearly everything plastic, if it isn't a bottle, pipe or profile, then it is almost certainly injection moulded. Injection Moulding forces molten plastic under great pressure into a closed Mould.
7. Expanded Polystyrene Moulding, where beads of polystyrene are treated to expand many times their size and fuse together in a Mould. Typical applications are the protective white blocks that new TVs come packaged in.
8. Slush Moulding where a liquid thermoplastic resin (usually PU I believe) is poured in to a hot hollow Mould and forms a skin on contact, excess liquid is drained off. I believe this is used in manufacture of automotive fascia panels.
9. Dip Moulding where a metal part, typically a tool handle is dipped into molten PVC which leaves a thin residue on the metal enough to make a cushioned handle grip.

There may well be other forms of plastic Moulding that I have not heard of or have forgotten about.

By the way, Moulding is not to be confused with forming, such as thermoforming or vacuum forming where an extruded (or liquid cell cast) plastic sheet is warmed and presented to a shaped surface in order to replicate that surface. Disposable yogurt pots are made this way. As are plenty of larger technical parts.

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