These two slang words are used all the time in spoken English and basically mean the same thing.
If something “blows” or “sucks” it means it is really bad.
Here are some real native examples:
This party really blows. Let’s think of an excuse and leave as soon as possible.
I really don’t want to watch that movie. I’ve heard from at least 5 different people that it totally sucks.
He seriously thinks he’s a good basketball player. I went to watch his game last night and he totally blows.
I love playing tennis but I really suck at it.
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