A little vapour from the exhaust on a cold morning is normal. Persistent or thick smoke is not.
Noting the colour, when it happens, and any smell helps a mechanic find the cause.
Thin white vapour
Thin white vapour that disappears once the engine warms is usually condensation and nothing to worry about.
Thick white smoke
Thick, persistent white smoke — especially with a sweet smell — can mean coolant is burning in the engine, possibly from a failed head gasket. Check the coolant level when the engine is cold, look for overheating, and get it inspected quickly.
Blue or grey smoke
Blue smoke usually means oil is burning. Causes include worn piston rings, valve seals, or a failing turbocharger. Check the oil level regularly, as the engine may be using more than normal.
Black smoke
Black smoke indicates too much fuel is being burned. On diesels, a little under hard acceleration can be normal, but persistent black smoke suggests a clogged air filter, faulty injectors, sensor problems, or a blocked diesel particulate filter.
CAUTION: This is general automotive information, not professional mechanical advice. Always follow your vehicle manufacturer’s specifications and service schedule, and have brakes, steering, tyres, and other safety-critical systems inspected by a qualified mechanic.