As I understand them, protein bits are like tetris blocks, and your goal is to make whole lines of them.
Animal products contains complete proteins - ie, a full line made up of different bits. Plants don't tend to, so you need to get protein from different sources, namely, legumes (which includes beans and peanuts), nuts, grains, seeds, etc. Some vegan complete proteins include soy milk, hemp powder, quinoa, and nutritional yeast.
Some combinations that make up whole proteins are baked beans on wholegrain toast (legumes plus a grain), nut butter on wholegrain toast, rice and beans, pasta and beans, houmous on pita bread, etc. You don't have to eat these combinations at the exact same time - later in the same day is good, too.
There's a better, more thorough, overview here, which doesn't once mention 'bits' or 'tetris blocks'.