The + and - on the Advanced page does mean "market price - the number you type in".
So if the market price is 855 (market price is the price of last executed order I guess) and you type in - 850 , you will place an order at limit price 5€/BTC.
Thank you for your explanation Serpens66 but it is still not totally clear to me.
What I really need to do it is SELL STOP LOSS LIMIT orders for my Bitcoin and it is possible doing them only in the advanced tab.
When you select this type of order the tab has already pre selected the "-" in the "Stop Price" row, the "+" is even not possible to select it.
If for example in the Stop I select the "=" and I type 800$ this means if the highest price in the Bids (Buying) of the Order book drop to 800$ or below (also "or below" right?) then sell the Bitcoins at for example 790$ Limit price.
Is this correct?
If instead in the STOP I select the "-"and as before I type 800$ as Stop and 790$ as Limit, what does it change?
And also in the Limit Price I can choose the "+-=", why?
If someone can please explain me also making a couple of examples with numbers, that's would be great.
Or else if can link me a place where i can read precise explanations, I mean i'm not lazy, I just need to learn because now i'm not able to set STOP LOSS LIMIT selling orders which can be pretty helpful.
I read the Kraken guide but it is not that precise and detailed in the explanations, it even don't mentions these "+-=" options.
It has nothing to do with stop loss or anything.
In you case, all you need is the "=", I would never use the - or +.
And yes, your example with 800 und 790 is correct. Just read the hint below the "OrderType you chose. If you choose Sell and Stop Loss Limit, then there is written:
"Sell at a fixed price once market price <= stop price."