"I use the train."
there are more terms depending on what you are looking for。
列車「れっ・しゃ」I think is more like "railway train", sometimes used as a general term、
汽車「き・しゃ」if you are looking for steam-based locomotives、
新幹線【しん・かん・せん】for the bullet train that connects with Tokyo、
地下鉄【ち・か・てつ】or メトロ for "subway".
You use wo for direct objects. Ni is used for location. In this case, tsukaimasu is the verb so you are "using the train". In other cases such as norimasu, you are riding "on" the train, so you use ni. Ha/wa is typically used for the subject. Watashi wa densha ni norimasu, for example.
Don't bother they don't always give you the audio for all the kanji. Especially if there is an alternative hiragana option or it is a kanji they have already drilled in practice many times but sometimes they make a small error here or there. Just use your time to keep studying. And practice your kanji like crazy. Repetition is the key.
The じしょーけい is 使う. In ます form it becomes 使います
つかい has the following definitions
Noun 1. errand; mission; going as envoy 2. messenger; bearer; errand boy; errand girl 3. familiar spirit Noun - used as a suffix, Noun - used as a prefix 4. use; usage; user; trainer; tamer; charmer