Hi,

If the attribute states are used along with a button, then the button only will be visible in the given state.

See the sample,

<button string="Confirm" type="object" name="confirm_resignation"
 states='draft' class="oe_highlight"/>

Now this confirm button will only visible in the state draft.

To hide the button based on multiple conditions, like based  state and some other field value,

<button name="invoice_print" string="Print Receipt" type="object" 
attrs="{'invisible':['|',('sent','=',False), ('state', 'not in', ('open','paid'))]}"
 groups="base.group_user"/>

If we simultaneously give attrs and states, states won't work. That's why states are given inside attrs

Thanks