I have really bad personal credit but I am seriously considering a bussiness to buy friom a friend
what does a bank look for in granting such a loan ?
will a bank secure a loan against the existing inventory of the store?

One thing they will always look for, no matter what, is a good, solid 5-year business plan. If you don't know how to do one, they have kits you can buy, or look it up online. Your loan will probably have to be secured by whatever inventory or equipment the business has.

Since you have bad personal credit, you may have trouble getting a loan to buy a business. Try banks first, but if you have trouble getting a loan, there are also non-profit organizations that specialize in lending money to new business owners just starting out. Try googling "micro loans" in your area. The interest rate will be higher, but they are typically good about working with you personally if you are struggling.