You must read Adalberts guide on ability. To simplify as much as possible:

Vets and experts are simple. If a sailor has zero vets and experts it has zero ability.

The raw ability numbers of your sailor assume a sailor with 100% of experts.

A vet counts as four experts.

So, in any particular category, the true ability of a sailor (assuming that that sailor
has 100% of allowed crew) is equal to:
True Ability = Ability * (Experts + 4*Vets)

So if a sailor has zero experts and vets then the True Ability on that sailor is zero.

What are the most common skills:
gunners:
accuracy ability affects spread (although the ship's fire control system and the gun's
inherent accuracy affect spread the most)
reload ability affects reload time. The more reload ability the quicker the gun reloads
versus its listed reload time. The listed reload time would be for a gunner with zero
true reload ability.

repair:
A ship's repair speed is based upon the sum of the true repair ability for all sailors on
that ship.

restore:
A ship's soft damage (SD) capacity is based upon the sum of the true restore ability
for all sailors on that ship.

engine:
A ships OH speed and OH time depends upon the sum of the true engine ability ONLY
for Engineer sailors loaded into support slots of that ship.

potential:
The shell spotting distance of the Bridge Officer is based on true potential ability of
the BO. In some ships this doesn't matter (CV's, subs and TW's) but in gunships it
matters a lot. You want to set the BO's true potential ability such that your shells
end at the end of the spotting lines. You adjust this by burning experts or shorting
the number of recruits (if the true potential is too high).

pilots:
aircraft ability at this time is not considered
bomber ability influences how much punishment a plane can take before being shot
down
fighter ability influences how much punishment a plane can give to other planes

France requires a bit of skill to play. If you are solid with IJN or KM play style, then
sure, pick France. If you want a nation that is still top-notch, then go with UK. France
is really a mixed bag of goodies. There are just as many pros as there are cons to
playing France. Whereas, with UK, the only con is probably lack of AA. But in return,
you're scoring the best repair/OH time the game can offer. If you have a lot of cash to
invest, even better.

To be sure, France is fun. But so far, the only practical uniqueness about French ships
is their size. Other than that, so far I haven't seen anything about the nation that
makes me want to get it over any other nation aside from novelty (except for IJN; that
nation just makes me cry).

Veterans are part of each sailor's crew that raises the true ability value for that
sailor. (i.e. more vets=more effective sailor)

The best gun varies from ship to ship, but there is a good beginner's guide stickied in
this section that can answer the basics of that question.

Subs have a unique play style compared to most other ships, and are generally considered
to be easier to play. If you have trouble with manual aiming or want to nuke bb5/6 in one
salvo then they are for you.

The "best" type of ship is always up for debate, but honestly it just depends on your
playstyle and what you have fun playing in.

I would skip the Simakaze and stick in Yubari as you get more experience in GBs in a CL
versus a DD. The jury is still out on the French Navy, no one is sure just how they will
stack up against the other 4 in the end, but they seem to have promise, so it might be
worthwhile if you're willing to invest the time in leveling.

A lot of the basics of nf:
trainworld.us/nf-guides/ (It's a mirror of nf-guides.com)

Ship and equipment info (often better updated than this site):
trainworld.us

How vets (and lots of other things) work: (Adalbert's guide)
http://www.navyfield.com/board/view.asp?Num=84358&Sort=D07
Short version: vets and experts make your crew more effective at their tasks, and 1 vet is
about as good as 4 experts.

The best guns vary with the ship and what role you want to take. Generally, you want to
maximize range (L version), and use the largest caliber guns that will fit. Exceptions
include using triple 6.1 or dual 7.9 N/D on the Agano and Mogami CL due to the L (and in
some cases N) guns not fitting, dual 5.5 instead of dual 6 (size and weight issues) or
single 7.9 (barrel count, rate of fire) on the Tsukikei and Yubari.

AAing will generally force you to smaller guns (dual 4.7 or triple 6.1 if you are using AA
gunners, dual 3.9 or 5 if you only have armament sailors, and dual 3.9 or triple 6.1 if
you are using regular gunners). There are good general guides stickied here, in the US
section, and at nf-guides.

If you want to go sub, those ship choices will work. If you're going for TW and ASW
(until you get that sub), consider running with very small or no guns for extra speed.