When co-signing on a loan you enter into an agreement to become responsible for the re-payment of the loan, including the late and legal fees, if the borrower defaults. However, the financial institution can lawfully go after the co-signer at any time.
If you do agree to co-sign on a loan for someone, you can request that the lender agrees that it will refrain from collecting from you unless the primary borrower defaults. Additionally, you can request that your co-signer agreement includes that your liability is limited to the unpaid principal and not any late or legal fees.
Upon co-signing you may have to provide financial documents to the lender just as the primary borrower and you will assume the same legal responsibility for the repayment of the debt as the borrower. Remember that any late payments will affect your credit as well.