Pail is another word for a bucket, particularly an old-fashioned wooden bucket.
Pain is a bad, distressing physical or emotional feeling. You feel pain when you are hurt or sick, or if something bad happens in your life like you break up with your boyfriend or girlfriend.
Paint is a liquid you can buy that you can use to change the colour of something. Paint goes on when it is wet, so you need to wait for it to dry. Some paints come in small, dry blocks and you need to wet them with water to be able to use them. You use a paintbrush to paint with.
A painting is a picture of something that has been made using paint. Paintings can be very realistic, almost as good as photographs or abstract and you have trouble telling what they are pictures of.
A pair of things is two things. You usually use the word pair to describe two very similar things, like a pair of birds. Some things only come in pairs - like a pair of glasses or a pair of trousers. Many other things usually come in pairs but can be separated, like a pair of socks, shoes or gloves.
Pajamas, also spelt pyjamas or just PJ's are clothes that you wear at night when you sleep. Pajamas can be worn by girls, boys, men or women, but nightgowns are only worn by girls and women. The lady in the picture is outside in her pajamas.