This screen is where you can summon heroes using different resources.
Gem Summon
Edit

The Gem Summon screen allows you to summon rare or ultra-rare heroes (3-stars and above).
Tap the 1 FREE Summon button to get a single rare or ultra-rare hero for free. Once you use this option, you’ll have to wait 66 hours before you can use it again. If you’d rather not wait, you can use a summon scroll to summon another hero right away
The 10 Summon option will summon 10 rare or ultra-rare heroes for 2500 gems.
Using either option will also net you crystals. Using the Free Summon or Scroll Summon options gets you 1 crystal, while using the 10 Summon option gets you ten crystals. Crystals can be used in the Divine House to purchase rare materials and heroes.
Friendship Pt. Summon
Edit

You can see how many Friendship Points you will be awarded in the Ally Assist screen, next to each hero’s Squad Level. Note that you will only be awarded those points if you win the battle.