Answer: I've visited three other countries: Ireland, England and France.
Explanation: Firstly when beginning a sentence it should start with a capital letter. The other punctuation correction is the colon between countries and Ireland; The colon is usually used in a sentence to introduce a list of things or objects or items. Sometimes a conjunction can be but in this sentence there was no conjunction between country and Ireland which made the sentence punctuation a bit incorrect so a colon had to be added. Nouns should also be written in capital letters, so Ireland, England and France should begin with capital letters. Hope this helps.