The first time you miss a payment, you'll probably be contacted by the lender to ask why. If you keep doing so, you'll be marked 'in default', which will appear on your credit report. This will likely prevent you from applying for more credit.
If you're ever struggling to make your repayments, contact the lender as soon as possible. This enables it to potentially help you – for instance, by extending the loan term, modifying your monthly repayments or temporarily pausing instalments. Do bear in mind that such measures may increase the overall cost of borrowing, even if they help in the short term.
Should you continue to miss your repayments and fail to let the loan provider know, it could take legal action against you. This can result in anything from repossession of your car to being made bankrupt over your debt.