"We found the new city."
Translation:Thángamar ar an gcathair nua.
@SteffaniesS, D'aimsíomar is to find or locate something youse were looking for. Thángamar is to find on purpose, by accident, or come upon by fate/destiny, etc. So both can mean finding a city, both can be finding it on purpose, only tar (thángamar) could mean finding it by chance.
teacht would be for Táimid/Bhíomar ag teacht ar... (we are/were finding...)
Which is a present/past continuous.
You chose "we were finding" instead of "we found". If you feel there is no difference, then do not worry too much: you just feel that in English you do not need to worry about grammar. And some people live a good life without worrying about grammar.
You could have gotten yourself understood with just "ag teacht ar", as long as you do not forget 'ar'. Duolingo will keep correcting you on the different types of past. Just ignore it if you feel it does not matter in English.