You will want to bring items along with your squad so that you can do additional healing, revive fallen units, remove bad status effect and many more. You can craft these items in Town via Synthesis. To craft your own items, follow these steps:
Item Synthesis Proper
1. Tap Town.
2. After opening your Town, tap Synthesis.
3. Then you will be showed a list of craft-able items. Tap the item you want to craft.
4. If you have the required materials, tap the blue Synthesize button at the bottom to create one of that item.
Notes to Consider:
1. You will definitely want to create items such as Cure, High Cure, Divine Light and Revive as soon as possible.
2. Be sure to read the Upgrading Your Town and Refilling Consumable Items article to learn how to level up your Synthesis to make more item and how to manage your item in your squad inventory.