MBK Center is a popular shopping mall in Bangkok. It's known for its wide range of shops selling everything from clothing and electronics to souvenirs and local handicrafts. The mall also has a food court with local Thai dishes and plenty of options for grabbing a cheap bite.
There are loads of shopping malls in Bangkok ranging from budget to luxury. Many locals spend their weekends in the malls because they are nice and air conditioned so they are usually quite busy.
If you need the Apple store or any international name brand products, heading to one of the malls in your best bet.