So I recently bought a new low-price laptop, Lenovo Essential B40-30. Specs are: Intel® Celeron® Dual-Core™ N2840 2.16 GHz processor, 14", HD, 2GB DDR3
I was wondering now if I could use Lubuntu or Ubuntu on it. I'm not sure about this because I checked the certified hardware for Ubuntu and the "essential" series isn't on the list, while "ThinkPad" series for example are. Is it even possible to install Ubuntu if its not on there?
Yes, the list of hardware with certified Ubuntu compatibility is not comprehensive. Linux and Ubuntu are meant to work on pretty much any PC but there's no guarantee for every available PC part. Especially new hardware often goes unsupported in Linux for a while (most manufacturers don't release Linux drivers so other people have to step in).
The manufacturers of the hardware simply decided to spend money and resources to thoroughly test it with Ubuntu and work together with the Linux developers and Canonical to assert that their hardware is most certainly compatible with Ubuntu. For instance, Lenovo (and formerly the notebook department of IBM) has employees that dedicate all or part of their time on the job to work on Linux support for hardware sold by Lenovo.