Where do I start?

Might be worth getting some Mackerel feathers and giving them a try
from the beach this summer. You will need a beachcaster rod with a
fixed spool reel and some feathers but that's about all. Alternatively
you could try float fishing for Mackerel and Garfish - a tackle shop
should be able to get you setup with the necessary floats and weights
for a few quid.

The great thing with sea fishing is you can spend as little or as much
as you want - don't let anyone tell you you need the latest and
greatest gear to catch fish - just start with the basics and expand as
you need to.