Put simply; a rectifier changes AC electric current into DC electric current.

There are several designs increasing in complexity and parts, but all are based on four or more diodes and optionally a capacitor.

single phase rectifiers

4 diodes

Standard textbook diagram of a single phase rectifier. the ‘~’ symbol is for AC input.

A single phase rectifier diagram. Drawn in a slightly different, but functionally identical way.

3 phase rectifier

6 diodes

A 3 phase rectifier. Shows that any number of phases can be used by simply adding two more diodes.

Here’s one I prepared earlier:

red labeled wires positive,  brown/black labeled wires negative, 3 other wires green individual AC phases.

2 BR 354 rectifiers used to create a 3 phase rectifier. A recycled computer south bridge heat sink has been cable tied on.

Rectifiers produce some heat while they are operational and require some cooling. Normally cooling is done by adding a  passive cooling block, thought fans may also be used.

Rectifiers need to be matched for the application based  on their voltage and maximum current.

The rectification losses are not large when compared to the reverse of the process; inversion.