modern (something)

"Modern" is an adjective that describes culture, fashion, ideas, technology, etc. It means "recent" - usually within the past 25-50 years, although for some technology products it can mean as recent as 2-3 years old like:

The computers at the library need to be updated to a modern operating system. They're still using Windows XP.

"Modern life" is a common phrase on its own. It means the way that people live in the present times.

confusing

Remember that when you're talking about a situation or topic, it's "confusing". When you're talking about your feelings, you say you're "confused".

(something) is (adjective), in that (independent clause)

You use this structure when you're describing something with an adjective, but you think your description needs more explanation. In the example sentence at top, you say that modern life is "confusing". But that could mean a lot of different things. Why is it confusing? Which part of modern life is confusing? Using "in that..." makes it clear what this means.

What follows "in that" is an independent clause, which basically means a whole sentence. This is a sentence:

It was announced 6 hours ago.

And here's that sentence used with "in that":

It's already old news, in that it was announced 6 hours ago.

This sentence (taken from a blog post by the musician Moby) is supposed to be a bit of a joke about how fast news spreads these days.

"In that" is used more in written English than in spoken conversation.

(something) is constantly (happening)

"Constantly" means "all the time" or "again and again many times". You use it like this:

She's constantly criticizing me. It's annoying.

The word "constantly" has a slightly negative sound. Even if you're talking about something that is usually positive, if you use "constantly" it seems like you might be a little annoyed.

People are constantly coming up to me and telling me, "Oh, you're so beautiful" but I'm like "Whatever."