Effect

[Dragontail]

How would I add an automatic critial to an attack?

ie. assinate allows for an auto crit if I go first and hit with attack.

[jshauber]

After the attack but before you roll damage, open the MODIFIER window (Top left of FG +/- symbol) and click on the critical button.

When you roll damage it should apply the affects of a critical hit to the target.

[darrenan]

Or hold down the SHIFT key while rolling damage.

[Dragontail]

is there a way to create an attack say

Rapier - rolls to hit and damage
and
Rapier Crit - rolls advantage and crit damage

without clicking extra stuff every time ?

[Trenloe]

Rapier Crit - rolls advantage and crit damage
Yeah, just add an extra attack action and drag another die to the damage dice section for that attack.

See this portion of the 5E user guide in the Wiki: https://www.fantasygrounds.com/wiki/index.php/5E_Character_Sheet#Creating_a_weapon Step 8 is when damage dice are added to the weapon entry.

[Zacchaeus]

is there a way to create an attack say

Rapier - rolls to hit and damage
and
Rapier Crit - rolls advantage and crit damage

without clicking extra stuff every time ?

You might be interested in this. (https://www.fantasygrounds.com/forums/showthread.php?27332-Effects-The-Complete-Rogue-Package) There isn't a way to fully automate this becasue FG can't know that you are rolling with advantage without you telling it, and similarly it can't know you get to roll critical damage under these circumstances (It will only know if you actually score a critical hit).

Having said that it's only one extra click (clicking on the ADV button down on the bottom left when you roll to hit) and as was pointed out above holding down SHIFT when rolling for damage forces critical damage to be rolled.