Your offer can include various conditions, which must be met before the deal is firm. Two very common conditions most first time buyers include are Home Inspection and Financing.
After the seller accepts your offer, you will need to get written confirmation from your lender that they will indeed lend you the money.
Only after your lender commits, in writing, to lending you the mortgage should you waive your finance condition.
It is important to have a qualified home inspector examine the house and provide you with a report outlining any problems. The inspector should look at structure all all major systems (heating, plumbing, electric, etc.).
An Insspection condition is usually included in your offer to protect you in case there are any major problems with the house.
Conditions need to be waived in order for the offer to continue forward. If you do not waive your conditions, the deal dies and the property goes back on the market. Buyers should only waive their conditions once they are sure those conditions are not longer a concern. For example, if you have a finance condition, you would not waive that condition until you had written confirmation from your lender that they will indeed loan you the money to purchase the home.