can someone tell me how to place a water purifirr

You have to craft it, make sure it's in your main inventory, select it, it will appear on the screen and you will get to choose where to place it.

Make sure you are putting it into your toolbar, then you select it by either the number key or by scrolling with your mouse wheel. Once selected, you can place it down.

It sounds like you were trying to drag it from the toolbar, or from the crafting menu "inventory". You do not drag things to place them, you select them from the toolbar.