How to use coal Ruby API in the wagon generated site? and other questions.

1.How to use coal in the liquid page?

2.Are there some REST API V3 (engine4 is v4?) documents?

3.How to use REST API V3 to create new entry that contains 2 belongs_to fields. What content should be written in the belongs_to field. (belongs_to user , belongs_to quest) , user_id and quest_id ?

3.1 tables: accounts , quests , quest_claims
accounts has_many quest_claims
quests has_many quest_claims
quest_claims belongs_to accounts , belongs_to quests

4.How to using REST API to get content entries applied more conditions (on the server side is better)
4.1. ex: get current user's claimed quests , expired quest , finished quests

Thanks