This is the 4899th most frequent Japanese word.
申し込ん
"申し込ん" is the stem form of "申し込む," meaning "to apply" or "to submit a request."
In this sentence, '申し込みました' (moshikomi mashita) means 'registered' or 'applied to.' It is used to indicate that the speaker has completed the process of applying for the mentioned entity, in this case, an online course.
私はそのオンライン講座に申し込みました。
I registered for that online course.
Here, '申し込んだ' (moshikonda) is in its past tense form and refers to the service the listener has applied for. This sentence is asking for details about the content or aspects of the service.
あなたが申し込んだサービスには何が含まれていますか？
What is included in the service you applied for?
In this example, '申し込む' (moshikomu) is used in its dictionary form to inquire about the process or required steps for registration to the event.