What is Retainer? Maybe you need get some basic information about it when you are in the level 20. Just like the following:

Around the level 20 mark in the main story quest chain, you'll unlock the ability to hire your very own Retainer. These are custom - made NPCs who can store excess items, sell items for you on the market and even be sent off on adventures of their own with Ventures. Once you unlock Retainers, you'll need to head to the Retainer Vocate in any major city. There, you'll get to customise them completely, just as you did with your character, assign them a personality, and give them a unique name.

From then on, you can summon your Retainer by interacting with a summoning bell, which are located in each major city, in your inn room, and some special encampments around Eorzea that are naturally highly populated. With an inventory space of 175 slots, they have room to hold plenty of items; even untradable ones. You can also store Gil on them too. Using them to sell items on the market will send any Gil straight to their storage for you to pick up later.

Retainer Ventures are mini - missions that you can send your trusty servant on. You can equip your Retainer with gear just like yourself, from combat classes and gathering classes. The better stats they have, the better rewards they'll be able to get from ventures. Here's a list of ventures you can send them on:

1.Hunting

2.Mining

3.Botany

4.Fishing

These will reward you with items related to the venture itself, e.g. Hunting will give you items that are found on slain monsters, whereas Botany will provide wood and plant material. There's also Exploration variants of all four mission types, which take a lot longer to complete, but give your Retainer much more experience before completion; perfect to set up before you go to bed. The Quick Exploration venture is the last of the lot - it will send out your Retainer to go and fetch a single item, but that item can be just about anything: from junk, furniture, to end - game gear.