It explains something that you normally do, but today you are doing something different.
Usually + Verb in a normal way (Present Simple),
but today + am/is/ are and the verb ending in -ing. (Present Continuous)
I usually play football on Wednesdays, but today I'm studying for an exam.
I usually go to school by bike, but today I'm not going because my bike is broken.
I usually eat spinach for lunch, but today I'm eating pizza.
You usually run 5 kilometres every day, but today you are running 10 kilometres.
You usually read 10 pages, but today you aren't reading so many.
We usually write a poem every week, but this week we are writing an e-mail.
We usually drink 3 litres of water, but today we aren't drinking as much.
They usually listen to pop music in class, but today they are listening classic music.
They usually pay in euros, but today they aren't paying in that coin.
He usually runs 5 kilometres, but today he is running 10.
He usually reads 10 pages, but today he isn't reading that number.
She usually writes a poem every week, but today she is writing an e-mail.
She usually drinks 3 litres of water, but today she isn't drinking that much.
The dog usually barks all day and all night, but today it isn't barking.
The cad usually climbs up the trees, but today it isn't climbing them.