You may have noticed Bricks are now dropping during PVP. Here's a quick noob FAQ.
What are they?
They are one of the two forms of usable currency for syndicates. The other is in game cash. One could argue gold is, too...but there's no in game option for donating gold.
What are they used for?
They are used to build/upgrade fortifications for your syndicate.
Why can't I view them in my inventory?
They're currency, like money or RP.
Why can't I buy anything with them, then?
Because syndicates aren't released. Once you get an app update that unlocks syndicates you will be able to donate them to your syndicate.
What are fortifications/syndicates?
Read The Billionaires Guide to Syndicates.
Edit: more questions answered.