When setting your Jomres based site up, first you should set your site's default language context. This is an option in the Site Configuration page of Jomres that allows you to define a basic language type to use. For example, if your site's used for renting out pitches in a camp site, then you'd set your language context as "Campsite". If it's for property rentals, then choose "Hotel". There are other options, but there may not be a language file in your language for that option, in which case you'll need to copy and modify the existing language files to suit your own requirements.
If you're going to be offering more generic options, then you can set the language context to the blank option, this will then refer to things like "businesses" instead of "properties".
Next, if they don't already exist, you'll need to create some business types. Several will have already been created for you when you installed Jomres, you shouldn't remove these until you're sure that you will not use them. If you're content to use the existing types, that's great.
If you're running a vehicle rental site, you'd probably want to emphasise that some businesses will deliver vehicles to the booker's home, or other such features. Create as many business features as you need, and assign them to the appropriate business types, eg "Vehicle Rental".
By default Jomres will create some room and property types that will be sufficient for somebody who's using the system to sell bookings in hotels or villas etc. If the types you need don't exist, you'll need to create some. For example if you're renting out cars you'd create a type called "Vauxhall Vectra", or "Ford Fiesta". If you are renting out multiple vehicles, then you would set the SRP only option to No. Remember to associate the resource type with your "Vehicle Rental" business type.