I give someone a sandwich and then say I wonder if the sandwich is o.k. He answers I like the sandwich, thank you.
In English we would only say I would like the sandwich if we did not already have it.
The two sentences are not identical in meaning.
Duo wants to you to learn the difference in French.
"J'aime le sandwich" is not placing an order with the server. It's just telling him/her that you like it. "I'd like the sandwich" is a contraction of "I would like the sandwich" which is the Present Conditional tense of the verb. In French, it is "Je voudrais le sandwich". You won't be learning that for a while yet. If you are serious about learning French, master the fundamentals. It will be easier for you later.
As you learn new nouns, it's always a good idea to associate the gender with it right from the beginning: the apple = la pomme (fem), the hat = le chapeau (masc); an apple = une pomme, un chapeau = a hat. Use a dictionary to look up words which are unfamiliar to you. You may be surprised to find many different ways a word can be used.
The verb "aimer" translates as "love" when referring to a person but "like" when referring to anything else.
If you say "Je t'aime" you are probably talking to a person so it will be "I love you".
So in the case of a sandwich "J'aime le sandwich" translates as "I like the sandwich".
If you want to say "I love the sandwich" it would be "J'adore le sandwich"
If you want to say to a person "I like you" you would say "Je t'aime bien"