Version:

This documentation is sourced from a third-party project and is not maintained by pgEdge.

Short Version

To compile assuming you have all the dependencies in your search path:

tar -xvzf postgis-3.5.5.tar.gz
cd postgis-3.5.5
./configure
make
make install

Once PostGIS is installed, it needs to be enabled (Creating spatial databases) or upgraded (Upgrading spatial databases) in each individual database you want to use it in.