How are free-trade area and a customs union alike and different

Free trade and custom union is similar based on internal arrangements.

Explanation:

In case of free trade no tariff is required but each and every member state is free to set their own external tariff. On the other hand the custom union is not having any tariff but all members of custom union has a same external affair.

In case of free trade all the barriers regarding trade among the member countries are not there. On the other hand the custom union develops a common trade with respect to the non members.

One of the example of free trade is NAFTA and on the other hand the example of custom union is single market.