It's like when you roll an r in spanish, right? like if you said "Burrito" you would roll the r (In REAL spanish not like ordering a burrito at the taco bell, be reasonable!), well a bilabial trill is like rolling a b. like what you do with your lips when you motorboat some fine big jugs, or play a didgeridoo, you know, whichever example you want. In the English language it just sounds silly in normal speech but some cultures admire it. whatever. its like saying to your bud, "YO BRAH!" but instead 'rolling' the b like, "YO BBBBBBBBBBBBRAH!"... get it? im not just talking out of my ass here, its a real thing. Check it out.
If you can imagine what the b sounds like then that's a bilabial trill!