The manual says "
The first training area on the list is Team Training, and this works a little different from the rest. When this is selected, the second menu lists three choices for training areas: Game Shape, Free Throws, and Stamina. For these attributes, it is easy for the coach to train all of the players on your team (he can have them shoot free throws for an hour or run laps around the building), and they dont depend too much on in-game practice. Therefore, selecting one of these options will train your entire roster, whether or not they play in any games that week."
Therefore stamina and free-throws are trained with no regard for minutes played if you use those training options.
In short, you have to spend a week training stamina specifically to improve it so it is a common pick for weeks like all-star week or post-season weeks where there is likely at least 1 less game worth of game-minutes available to you to train players in other skills.
Game-shape is actually what is affected by how many minutes a player plays. It seems to be generally agreed that the nearer to 60-65 minutes played each player is that week, the more likely they gain gameshape and the more gameshape they gain. If the player is MUCH higher or lower, they will lose gameshape and usually quicker the further they are away from that sweetspot of the amount of minutes played.
Training speed is affected by multiple things. If you train a skill for 1 position you train less players but the players you do train improve quickest, 2 positions a bit slower training but for more players, same but even more so for options that allow 3 position training, and when you choose to train a skill and that skill (passing or rebounding for example) gives an option for the whole team then that is slower still but everyone that hits their minimum minutes get some improvement in that skill.
The manual again about the training minutes :- "
How many weekly minutes each age group need for full training?
18-19 years old: 45 weekly minutes.
20-26 years old: 48 weekly minutes.
27+ years old: 40 weekly minutes.
Note: One minute buffer is placed for all age groups, which means 44 minutes is also sufficient for 18-19 age group."
You therefore can only get so many minutes at a position each week for so many players so how many positions you train and in what skills is a judgement call for yourself every week and depends on what you are trying to do.
Younger players train quicker than older players (losing a few% in training speed every year older they are), shorter players train guard skills (like jump range and outside defence) quicker and taller ones train forward skills (like rebounding or inside shooting) quicker.
You can improve training speeds by buying higher level trainers (small bonus to all players who get minutes), or a youth trainer (ONLY gives bonuses to 18&19 year old players who get minutes). There is also a gym you can buy (in the arena section), but most managers (including me) would recommend building up the arena capacity first for any newer team. Gyms have a sizable building fee AND weekly maintenance costs. Trainers can also be quite expensive, you likely want the arena capacity early to pay for stuff like that later!
If you haven't already then watching this video may be useful
https://www.youtube.com/watch?v=yN_0E74KkqYThere are plenty of other aspects to training but that should get you pointed in the right direction until any other more experienced manager turns up to answer.
Lastly, experience can't be trained & only gained. The more games you play, the more you will see players go up a level in it. As you can't do much else other than pick players consistently to raise it, I wouldn't be specifically concerned about that yet and concentrate on things you can control like training minutes!
Hope this helps.