lavaan is implemented as an R package. This means that before installing lavaan, you should have installed a recent version (>= 3.5.0) of R. You can download the latest version of R from the R-project website.
Once you have installed R, you can install the lavaan package simply by starting up R, and typing
install.packages("lavaan", dependencies = TRUE)
To check if the installation was succesful, you can load the lavaan package and try one of the examples. For example:
If you can see the output, everything is set up and ready.
Now that you have installed lavaan, you can: