“But sometimes you'll be flipping through the channels and come across something really interesting.”

You're in a conversation with a group of friends about your TV-watching habits. You like having cable on your TV because you can find interesting shows to watch. You explain this to your friends:

But sometimes you'll be flipping through the channels and come across something really interesting.

Sometimes (someone) will be (doing something) and (something will happen)

This phrase describes a situation that sometimes happens. It uses the future tense "will", but it doesn't describe something that happens in the future. Instead, it's something that has happened in the past several times and might happen again. Here are some other examples:

Sometimes I'll be sitting in my office and Nadine will yell out a question to me from the office next door.

You know how sometimes you'll be driving along and another car will pull out in front of you all of a sudden? That makes me so annoyed.

flip through (something)

To "flip through the channels" on your TV means to change the channel again and again to search for something you want to watch. You can also "flip through" other things:

• the pages of a book
• CD's in a music store

come across (something)

This phrase means to find something without really trying to look for it:

I came across an article on the Internet the other day about how sitting down for long periods every day at work is really bad for your health.

Aren't these great? I came across them at a thrift shop a couple weeks ago.

something (adjective)

Call an interesting thing "something interesting". Call a frightening thing "something scary". "Something ___" is more natural than saying "a ___ thing".