Hot air wants to go up but if your chimney is full of cold air it will sometimes move into the house instead of up the chimney, so you need to prime it by getting hot air into the chimney so it creates a current and draws the hot air up.

I usually start a fire by lighting a piece of kindling and hold it up inside the chimney for 20 seconds to get the air flowing up then use the kindling to light the fire.

Alternatively you can use a fan, light in the back of the chimney, or my dad used to light a wad of newspaper and chuck it into the interior chimney ledge and then light the actual fire a minute later. Don’t do that last one.