Loosing a button is easy to fix unless you find yourself without an extra button or thread.
Many garments have extra buttons on them when you buy them. On a shirt you can find these buttons along the hem of the garment usually in the front. They are sewn on the inside of the garment so you cannot see them on the outside. On pants you can find these extra buttons inside the waistband usually on the front.
If your garment does not have extra buttons sewn on it see if you can find the original to sew back on. If you can’t find a extra button then try to find a close match. The new button should be the same color and the same size to work.
Next find some thread that is the same color as the thread that the button was originally sewn on with. You will also need a needle that will easily fit into the hole of the button.
Thread the needle with a piece of thread that is about two feet long. Once the needle is threaded knot the two ends together so your needle has double thread to sew the button on with.
Put the needle into the back side of the garment where the original button was and pull it through to the front. You should have a threaded needle where the button belongs. Then place one of the buttons holes back side onto the needle. Put the button on the thread right up against the garment and place the needle into another hole right through into the garment.
Your needle should be on the back side of the garment and the button should be on the front side with one thread holding the button on.
Next put the needle into the back side of the garment right into the first hole and pull it through to the front. Keep putting the needle through the button holes through the garment from the front to back and back to front until the button is sewn on at least four times. Then put the needle and thread through to the backside of the garment if it is not already there and knot the thread. Cut the needle and extra thread off.
If your button has more then 2 holes you will need to repeat the process with the other remaining holes. If you are confused take a look at another button that is already sewn on. Your button that you sew on should look similar.