The Treasury corresponds to all the tokens owned and managed through the proposals by the DAO.
Shares & loots corresponds to the rights on the tokens in the Treasury.
Thus, the Treasury can be considered as a balance sheet, with tokens as the assets and shares & loots as the liabilities.
De facto, all the members who have shares or loots own a pro rata share of the Treasury. The percentage of Treasury owned corresponds to the shares & loots owned by the member divided by the total number of shares & loots in the DAO.

ERC-20 Tokens

The Treasury manage ERC-20 tokens. Every token has to be whitelisted, i.e go through a whitelist proposal.
The DAO creator can set an initial list of whitelisted tokens without going through a whitelist proposal
ERC-20 tokens are considered as fully liquid, i.e withdrawable by any member who Ragequit or is Guildkicked of the DAO.

ERC-721 Tokens

ERC 721 Tokens management is yet to be implemented