Gear with skills

If I have a piece of gear that adds a skill - I.e level 7 lightning blast - not sure if that is a real skill but you get the point)

If I have that weapon with said skill equipped will I then have access to that skill like I would with a skill gem in the skills area so that I can add other gems to make it better…I.e concentrated affect etc)

Yes. If you have equiped a weapon with a skill (same with shield), a line with that 'skill' will be visible to let you put support gems into it.

As for having more sockets into those skills, it is linked to the level of the item. You cannot use a jeweller orb on the skill from a weapon to have more sockets.