Translation:I take the subway.
I wish the app was more accurate with the translations. If のりmeans Ride, then it shoud translate as so. It reminds me of the English term "taking a pee." If you think about the verb literally then it seems like you are cupping your hands underneath a stream of urine, catching it, and then running off with it. "Muah haha. I took this pee!"
But you see, in another thread it says タクシーに乗ります (takushii ni norimasu) and it's translated as "I ride a taxi", so everyone is complaining because no one says that in English, you say "I take a taxi". I prefer literal translations as well, but either way someone is not going to agree.
About the rest of your comment, I shouldn't have read it at work because now people are wondering why I'm making such a strange face...
It means to get on/to board/to ride/to take. You use it both to refer to the act of getting on the (bus/train etc.) as well as to refer to action of the journeying in that vehicle. In a way you both 'noru' on to the bus and 'noru' in the bus. In contrast with 'oriru' you simply just get off (exit) the bus, it doesn't also refer to the actual journey as well. I think this is why you use the particle 'ni' with 'noru' and 'o' with 'oriru' in this situation. If that helps at all? You definitely aren't wrong but there is further usage and meaning behind noru :)
I think that would be something like 地下鉄に乗って (chikatetsu ni notte) - imperative tense. Now, I'm pretty sure this would be rude without ください on the end (maybe also just ungrammatical), but to my American ears it feels strange to give directions with the vague equivalent of "please" on them. "Please take the subway" almost feels ruder, like "get away from me".
But kudasai doesn't mean "please" really, I guess it's more like "You are welcome to use the subway."
In short, my best guess is 地下鉄に乗ってください。