Starting Unit Guide - this GoogleDoc will give you an idea of which units you may want to prioritize early on and whether you should consider rerolling
Reroll Guide - if you are trying for an optimal start, this guide will explain the process of rerolling and give some idea of which units to look for
Milestones - milestones are one of the main reward systems in the game, this explains the various types
Daily Milestones - these are generally recommended to do every day and are your primary source of AP
Story Quests - these quests will give you many rewards through milestones and challenges, as well as provide access to good equipment farming quests and hard quests for farming character shards
Challenges - these are an additional reward system you can progress through when doing story quests (the 6th challenge board gives a 5 star unit selector)
Farmable Character Shards - lists which character shards currently can be farmed through hard quests and where to find their quests
Event Quests - these quests are a mixture of limited time events and some permanent quests that are separate from the main story
Multiplay - many event quests have a multiplayer version (new players get 25 gems from the first 10 players they meet in multiplayer quests)
Arena - this is an additional source of daily gems (for new players it's recommended to deliberately climb the arena ranks slowly to maximize gems)
Mystic Tower Veda - this is a special event available periodically (usually once a month for 2 weeks) that you can slowly progress through to receive significant rewards
Summoning
Acquiring Gems - reference on the various ways in the game to collect gems for summoning
Spending Guide - reference on how to best optimize spending of real world money in the game, including tips on ways to purchase gems without spending money
Other
Friends - explains how the friends system works (a key source of mercenaries and friend coins)
Shops - some information on the various shops available and what you can get from them (for new players the beginner shop is a high priority and monitoring other shops for equipment can also be useful)