How do oil paint and water paint differ?

Now - what are you asking? The difference between regular oils and ones you can use with water? The difference between oil and acrylic? Or between oil and watercolour? If we DIDN'T know the difference, we wouldn't be here on POL. If you mean the most obvious, the difference between oil and watercolour, it's about opaque paint on the one hand (usually) and transparent paint on the other. Usually, you start an oil with darker colours on a tinted background and work towards light; whereas with watercolour, you work (normally) on a white background with your lighter colours, and gradually strenghten them in washes: although there's more than one way to apply watercolour. If you mean the difference between oil and acrylic, or regular oil and water-miscible (that is, it's mixable with water) oil, that's a discussion you can find if you look on the older threads. If you'd like to tell us exactly what you have in mind, it would be easier to answer you.

Semb has posted before keora but it seems he wants to be taught everything about painting from scratch - it might be best if he started the basics with a good book.

Keora - we've all asked ourselves the same questions about Semb and others - but I operate (when I've the patience) on the basis that he might be genuine, and curious; and hope that by replying I can persuade him to tighten up his questions so there's something to get our teeth into. It also does no real harm to go back to basics now and then - but there are limits to my gullibility..... and I'm approaching them.