"Heroes" functional allows you to improve the hero and recruits.
Boost
To increase experience of your hero press the [Get EXP] button, by clicking it you can enter Temple of Trials.
Of course you can get experience for your hero in other server events.
To increase your heroes's experience you'll need Elixirs of experience or Exp. Potions. Select recruit who needs to increase experience and you use necessary quantity of elixirs of experience, further press the Boost button.
Be attentive: besides elixirs of experience dimes are spent, their necessary quantity is displayed in the line "Expenses".
When there's enough experience for your recruit's improvement, the system will notify you that the current recruit has reached a maximum level and his/she needs to upgrade.
Upgrade
For an upgrade of your hero and recruits you need special objects, for example, Star Shards or Ice Crystals, which can be received in Temple of Trials or in Exchange store.
When you have enough objects for improvement and the hero will reach necessary level, you will be able to improve your hero to the following class (blue, green, violet, etc.)
If you have 2 or more identical recruits, you can click "Dismiss" and get some Hero soul points. But don't hurry to do that, cause for further improvement of your recruits you'll need recruits of the same type. For example, if you need to improve Fist of Judgment to orange level, you need 2 Fists of Judgment of maximum level.
Recruit
"Recruit" function allows you to recruit heroes for certain amount of Dimes. You can receive unlimited number of identical recruits, but between hiring there has to pass a certain amount of time.
Group
To make a Group click "Group" button. 
Here you can create a line-up that you need for your battles.
To add hero to a group click on his image on the left and choose a position for him in opened menu. To remove a hero from the group just click on him in the main window of line-up.