Suzie explained it really well, but if any of you want to look it up this website is pretty good at explaining as well: http://www.babycentre.co.uk/baby/startingsolids/babyledweaning/
The thing with BLW is that you really have to wait until 6 months, and even when you wean most of the babies nutrition still comes from breastmilk/formula. When they are offered food at first they will probably only lick and suck bits and not actually "eat" much, and the food you give is just what you would have. My friend gives her little one home made potatoe wedges, carrot sticks, humous, omelette etc.
With purees they get much more down them, because its mashed and fed to them. I think you can also start earlier because you start with very smooth puree and then progress to more lumpy foods, but Im not sure, as I think the guidelines are still 6 months but very few wait until then.
They say BLW stops babies from being fussy as they are in control of what they eat and how much they eat.
xxx