If you go to the "Training" page, you can set the training schedule for your team. NOTE that this is possible only if you have at least one coach. 

If you have none, the players still train. (They just train under an amateur coach and hence, advance more slowly than they would with professional coaches.)

We'll start with Training.

Firstly it is very good to know what each bar you have corresponds to. So here is a list.

Strength - This will improve Natural Fitness, Stamina, Strength and Work Rate.
Aerobic - This will improve Acceleration, Agility, Balance, Jumping, Pace and Reflexes.
Goalkeeping - This will improve Aerial Ability, Handling, Kicking, Throwing and One on Ones.
Tactics - This will improve Anticipation, Decisions, Positioning, Movement, Teamwork and Command of Area.
Ball Control - This will improve Dribbling, First Touch, Technique, Flair and Heading.
Defending - This will improve Tackling, Marking and Concentration.
Attacking - This will improve Passing and Vision.
Shooting - This will improve Finishing, Long Shots and Composure.
Set Pieces - This will improve Crossing, Corners, Freekicks, Penalties and Long Throws.
Let's start with the most important position on the field.

Goalkeeper

Strength – Very light amount of this is needed, don’t need to be very fit, strong etc.

Aerobic – Quite important, suggested to go to medium amounts, as goalies need to be Agile, Balanced with good jumping and reflexes.

Goalkeeping – Must be as high as possible (for obvious reasons)

Tactics – Light / Medium need for all parts that this improves.

Ball control – None of this is needed. Goalies aren’t known for there amazing ball control skills.

Defending – Very light amount needed. They may only need a bit of concentration, otherwise they do not bother to put it in.

Attacking – Nothing needed, as they don’t attack.

Shooting – Nothing needed, as they don't shoot on goal.

Set pieces – Light amounts, they don’t need to much of it.

Defender

Strength –Medium amounts needed of this, They need to be strong and quick.

Aerobic – Light / Medium amounts of this needed, especially for jumping attribute, important when defending.

Goalkeeping – None

Tactics – Light / Medium need for all parts that this improves again.

Ball control – Very light amount needed, just good for heading really.

Defending – Heavy amounts needed.

Attacking – Very light, if any at all, they don’t get into attack too much.

Shooting – See above.

Set pieces – Light amounts, mainly as they can be useful for long throws.
Midfielder 

Strength – Again, Medium for a good holding role.

Aerobic – Light / Medium need for all parts that this improves again.

Goalkeeping – None.

Tactics – Light / Medium need for all parts that this improves again.

Ball control – Light / Medium needed, depending on how you play the DM. If you play them more attacking, then put this up, if not, put it lower.

Defending – Light / Medium needed, depending on how you play the DM. If you play them more attacking, then put this up, if not, put it lower.

Attacking – Light amounts needed for this, again depending on how you play your DM.

Shooting- None really needed to be honest, they aren’t used as finishers.

Set pieces – Light amounts again. Unless u have midfielders that take free kicks
Strikers

Strength – Light / Medium because they need quite good natural fitness and stamina

Aerobic – Medium for the needs of pace which is extremely useful

Goalkeeping – None

Tactics – Medium, this helps them get into better positions I have noticed, which creates more, and better chances.

Ball control – Medium, for the same reasons that Attacking Midfielders need it. Maybe a bit less, as they don’t need as much flair in the game.

Defending – None

Attacking – Light / Medium Helps out strikers but not dramatically

Shooting – HEAVY amounts, intense if possible.

Set pieces – If you prefer to use strikers for corners etc. put this on Medium. If not put this slightly below medium, for penalties.

Let's start the talk about Coaches:

Now, about those coach "fields": as you can see, all the relevant coach attributes are displayed in the top of the field and there are two drop-down menus below.
The first one is the "Focus on" drop-down menu. It contains:

* General training - The coach teaches everything in small doses.
All the attributes can be improved.

* Goalkeeping - The coach only trains goalkeeping skills
Reflexes, One-on-Ones, Handling and Communication can be improved.

* Defence - The coach only trains skills needed in defence.
Communication, Tackling, Heading and Marking can be improved.

* Midfield play - Coach concentrates on the skills needed in the midfield.
Passing, Crossing, Long Shots and Creativity can be improved.

* Attacking - The coach teaches skills that are needed to score goals.
Shooting, Dribbling, First Touch and Heading can be improved.

* Fitness - Coach concentrates on getting the players fit (if you have a fitness studio/centre you get a bonus here).
Speed and Strength can be improved. The player's Condition also gets a small boost

* Train Youth Players - This means the coach will train the youth players.
You cannot give him instructions as you would give the coaches who train the players in the 1st team.
Train Youth Players means that the coach trains them in everything. How good that is depends on his attributes.
NOTE that the "youth" coach will not be able to train your senior players.