I bank with Barclays, and there are a couple of ways to check your balance online:
1. Use the website at Barclays.co.uk (or use whatever top-level domain corresponds to your country - so, for example, if you are registered with a Barclays Bank in Italy then visit Barclays.it).
You'll be asked for a few details to prove who you are, and you many need your PIN sentry handy.
2. You can use the Barclays app. I'm on iOS so I would download it room the app store, but I'm pretty sure it's available on Android too.
It's free, but may you'll need some bank details at hand to get set up.
Barclays also has an app for quick money transfers over the phone called
Ping It.
To get your account ready for mobile or internet banking, you sometimes have to activate it by speaking to someone at the bank. They're also pretty good at assisting with questions too.