Trade barriers come in a lot of forms. Quota is one. This is when a country sets a limit to the imported products. This is completed for a number of reasons. One is due to the government of the importing country wants to protect the local manufacturers.
In this way, trade barriers can affect the international trade due to it does not promote free trade. When countries trade with every other they do not want to have trade barriers due to it can result in an unfair trade where country A may export goods to country B but country B cannot do vice versa because country A sets up trade barriers such that it makes it very complex for country B to export.