All drinks are based on a shot of coffee - that being 30ml of espresso (at which point blonding will occur if your tamp is correct) to which you add the frothed milk.....
A cappuccino (in a "normal" cup) requires a double shot of espresso so that it is 1/3 espresso. 1/3 milk and 1/3 milk foam.
A "weak" cappuccino only uses a single shot.
A flat white is also a shot of espresso with the rest milk but only 1 to 1.5cm of milk foam....
NEVER...NEVER extract more than 60ml from a double basket...
A flat black for example is a double poured into a cup of water at about 93 deg c.... not a cup extracted through the puck. That would taste like cr@p!!!
The recommended tamping method - as demonstrated at a commercial barista course is :
grind through the doser (dont leave grinds in the doser - they are stale in 3 minutes!!) into the basket.
Turn off the grinder when the basket is almost full.
Tap the PF to settle the grinds
Empty the rest of the grinds from the doser into the basket
Tap to settle
Level off to the top of the basket
Compress very slightly with the tamper and then tap the edge of the basket to remove any grounds around the edge (if the tamper is not a tight fit!)- these stray grinds will fall back into the basket.
Tamp once (and once only) to 30 lbs (about 15 Kg)... (practice using bathroom scales)
Load, lock, extract..
Hope that helps.