ooohhh I understand :) Thank you so much !!! ありがとうございます！！

カタカナで書けば、多分、 can＝カン・キャン can't＝カント・キャント、そして「ト」から「オ」を引く

Yes, there is a difference between can and can't. can't = the negation of can and is short for cannot. So I can lift the bag. I cannot lift the car == I can't lift the car. How to describe the difference in sounds ? That is a really hard thing to do ! You saying " can ' T" would be a different sound than "can't" can ' T = both the "can" and the "T" would be separate word with equal stress on both parts. can't = is more aspirated with the t portion of the sound descending in volume. Because I speak English with an accent similar to that of South-East England, my pronunciation would sound something like "kar'nt" with the t sound at the end dropping rapidily in volume -- almost like clicking your tongue and breathing out. English speakers from the US and Canada might sound very different. And (just so you know) speakers from England may say that the English spoken in Australia sounds very different -- they can explain the difference if they hold that opinion :-)

yes there is a difference