We do not write detailed guides for things that are already available on their own source documentation, such as what Sponge is or how it works, and are not directly anything to do with us, - as such we only provide guides on how to install SpongeForge/set it up on our servers.
If you want detailed guides for Sponge such as how it works or what is they will have their own documentation on this for you to read.
The installation process is correct in our guide - you simply set up the relevant Forge build, add the SpongeForge mod jar to the mods folder and any Sponge plugin files you wish to use to the mods folder and restart the server.
Their own guides for SpongeForge are no different, there are no other ways to set it up serverside. The only part of their
installation guide that is relevant to the server installation is what we have in our own guide, as their steps on installing Forge itself are not correct for shared-hosted servers (it is installed as per the
Forge installation guide or by using the options available on our 1-click install list), and you simply add the SpongeForge mod that is compatible with that Forge build to the mods folder as with any mod.