Parameters give different options to the command. Some commands take only a long form or short form, sometimes both, depending on the creator.
Single Letter Parameters
Single letter parameters, like ls -a, use a single -. To combine multiple parameters, chain them behind the single dash, ls -al, or use a new dash for each, ls -a -l.
Full word Parameters
The longer form requires -- before the flag, like ls --all.
Help
Searching the web can show the parameters, but most commands include a built-in help page, accessible with -h or --help.
Most tools also include a manual page which can be viewed with man: man ls. The manual page normally gives full listing, rather than limited breakdown of --help page.