Hi Deryn
I used to work for a fostering agency so can only talk about what we did. It will also vary depnding on whether you are employed by a private agency or a local authority. (My feeling is private agencies train over and above the LAs. The children placed with you have a social worker and you have your own social worker).
You and anybody living in your household will be investigated fully (CRB checks, local authority checks, medical and another one I can't remember - it is 2-3 years since I worked for them!)
A social worker will interview you, talk about your family, your childhood, your experiences, your support network etc. This will take place over a few months. You will get a no-holds-barred 'introduction' to fostering so you know exactly what you are getting in to. your house will be inspected and safety features have to be in place.
You will have to have a spare room per foster child (some authorities will allow one room for two siblings of the same sex).
When the application process has been gone through you are invited to attend a panel meeting. The panel are independant specialists who will have read through your application, your assessing social workers reports etc and will then decide whether to approve you as a carer and for what ages/sexes.
Children being presented for fostering tend more and more to be 7-8 years old upwards. There are very very few babies put up for fostering. Many of the children - if not most - have witnessed some terrible things which does come out in their behaviour. During the application process you will be able to state what would not be acceptable to you.
If you decide to become a carer and are accepted then you will be contacted when a child is put up for fostering that your agency thinks you would be suitable for. They will give you a few details about the child based on which you say whether you wish to be considered. Your details are then forwarded to the local authority who decides yes or no.
That's all I can think of off the top of my head!