An English word (adjective and adverb) that can cause confusion for second language learners is overseas. It is generally used to mean foreign, although the dictionary definition is a place that you have to go over a sea (or ocean) to get to. Since the United Kingdom is an island, this association is natural. The word overseas can be used both as an adjective and adverb. However the word foreign is only an adjective. The word abroad is usually used as an adverb with the same meaning as overseas. However the word abroad is occasionally used as a noun or an adjective.
I went overseas to find work. (overseas as an adverb)
I went abroad to find work. (abroad as an adverb)
I returned from abroad. (abroad as an noun)
I was hired by an overseas university. (overseas as an adjective)
Thailand is a foreign country. (foreign as an adjective)
Australia is an overseas country. (overseas as an adjective)
He is a foreigner. (foreign in the form of a noun)
This confusion of meaning can spill over to other meanings. Is the United States both a foreign country and an overseas country to someone from Canada? It is at least international, because it is a different country. Even then the meaning can be confused. The picture below of a Canada Post publication has an English error no matter how it is judged. Any mail sent to The United States from Canada is international mail. This error suggests that Canada is part of The United States of America, which it is not. Although maybe Canada Post's writer would like a different political situation.
There are some older twists to the way the words overseas and foreign are sometimes used. The word overseas is a compound of over + sea. However it was popularized during World War One when it was used as a British euphemism for the word colonial, which was no longer polite. So New Zealand was not foreign, but it was overseas. The word foreign specifically refers to a country not your own. However it used to be more related to language, not territory. Hence in the UK, Americans might not have always been considered foreigners, although they are overseas.
By modern usage, an American going to Canada is visiting a foreign country, but arguably is not going overseas. An Englishman going to France is only crossing the English channel, the channel is a sea, just not a very wide one! So the word overseas is still used. A Canadian going to France is going overseas and visiting a foreign country. In common practice today overseas is a synonym for foreign. However sometimes meanings are confused.
Originally the word abroad meant widely apart. It is still occasionally used to mean over a large area or number of people and was similar in meaning to out and about or “at large”; Example: Ebola is abroad in western Africa. These uses are less common today and can usually be avoided.
I have no easy solution for you; just be warned that the meanings of these words are not universally agreed upon. England is on an island, and when used as an adjective, overseas and foreign are usually used as if they are interchangeable. India is foreign, but not overseas from China. To avoid confusion it is better to avoid the words overseas and abroad.