The package manager is called zypper. Here are some useful commands

zypper search gcc --  Search for string gcc
zypper info   gcc --  Show description for package gcc
zypper refresh    --  Update package description from repositories
zypper lu         --  List upgradable packages
zypper up         --  Upgrade packages
zypper dup        --  Upgrade distribution

We will install most softwares using Spack. But first we need to get some basic stuff from Suse

zypper install gcc
zypper install gfortran
zypper install gnuplot

After this, see the Spack page on how to install scientific softwares.