Due to the UK being shut off from the European mainland because of the new Covid-19 mutation it is very likely your order will be delayed until further notice. There is nothing we can do about this at this point in time
The bottom bracket is the part of the bike that is all about it. The cranks are attached to the pedals at both ends of the axle. The same applies to the front sprockets. In Frank's assortment you will find bottom brackets from, among others, Shimano and Neco.