Opening applications can be done in several ways.
The most beginner friendly one is probably the graphical launcher. It is accessed by clicking on the desktop or status bar, pressing space on an empty tag or with Super + y. You can search through applications and press return or click on them to launch them. More frequently used applications will appear further up in the list.
Technical note: the graphical launcher uses xdg desktop files for its entries, meaning that only applications that provide such files will appear. This is the same principle found in desktop environments such as gnome.
Text based launcher
There is also a smart text based launcher. It can be accessed using Super + Space or by right clicking on the desktop. This launcher is using $PATH for its entries meaning that pretty much all applications are accessible from here. That includes applications that do not open any windows like grep or htop. Just like the graphical launcher this launcher remembers frequently used applications and puts them higher up in the list. This launcher can also be used to run applications with specific arguments or from absolute paths.
It also has a few different modes. You can switch between them using Shift + Left/Right Arrow The default normal mode is using $PATH and executes the given application. The terminal mode works just like normal mode but launches the application inside of a terminal. This can be useful if you want to check the logs of a GUI application or want to open a CLI application.
The third mode uses the xdg desktop entries as the application list and can be used to launch programs that do not have an entry in $PATH like some proprietary programs and wine programs.
dmenu like menu
This behaves exactly like dmenu. Nothing special about it. type in a command and press enter to run it. It can be accessed Super + Ctrl + Space or by middle clicking on the desktop.
my program doesn’t appear
some programs, mostly proprietary ones install to locations outside of $PATH and Windows programs installed using wine. As an example, Davinci Resolve installs to /opt which is not part of $PATH and does not appear in the text based launcher. It does however provide a desktop file meaning that it is accessible from the graphical menu. Some applications do not provide desktop files at all and are installed into directories not included in $PATH. In that case you can either add that directory to PATH or execute the program using its absolute path. In the case of Davinci resolve that would be /opt/resolve/bin/resolve. Wine programs can directly be invoked using wine /path/to/program.exe
dafuq is $PATH ?!
$PATH is an environment variable containing a list of directories. If you execute a command then Linux goes through all those directories and checks if any of them contain an executable with that name. It then stops and executes that application.
None of the launchers are present on my system
You likely installed instantWM on an existing system. instantWM is just a window manager does not include any other programs. These have to be installed separately from http://packages.instantos.io.. It is also a lot harder to provide support for these frankensteined systems since lots of things can vary depending on what your base system looks like.