Hopefully I can add something here, making the answer non-duplicate.
In regards to 'need to add sugar', it is much better to let the yeast ferment everything that they can in the beer, and then add a measured amount of additional sugar. The other choice is to try to predict where the yeast will actually stop, which requires accurate measurement of sugars, great familiarity with your yeast, and every other variable like temperature and yeast health being totally consistent. So, almost nobody bottles with the intent of carbonating from the original fermentation.
Beside making additional carbonation, the sugar that your father mentioned will result also perk up the yeast a bit so they can consume oxygen that got into the bottles. In this way, the added sugar is actually protecting the flavor of your beer.
As to what kind of sugar you use, or how you add it, there are several choices.
It terms of how, I suggest boiling a measured amount of sugar and stirring it into the beer with gentle stirring. This sanitizes the sugar and will be very consistent if you stir enough. Don't worry about getting a little into suspension, it will fall out soon enough.
In terms of the choice of fermentable sugars there are many to choose from:
- Corn sugar (refined, mostly glucose, sold as 'brewer's sugar', 100% fermentable)
- Table sugar also works (refined or not, mostly sucrose, ~100% fermentable)
- Honey (100% fermentable)
- Dried malt extract (less than 100% fermentable)
- Wort from your next beer (variable fermentability)
- Fruit, candy, whatever...
The amount you'll want will depend on the style and/or your preference, but expect 100-200g of fermentable sugar in a 20L (5 gallon) batch. 1.25 cups of DME is an popular way to keep it all malt (see any Papazian book).