I don't know how much sugar I use in tea for a gathering. Because some are like more sugar and some less. So how can I manage sugar in tea?
In the Western culture it is common practice to prepare tea without sugar and then add an individual amount of sugar in the cup.
At a larger and informal gathering where guests serve themselves, you would provide a pot of unsugared tea and a pot of sugar with a teaspoon in it. You also provide a teaspoon to each guest. The guests use the teaspoon in the pot for pouring the sugar into their cup and use the personal spoon for stirring.
If you want to be an extraordinarily accommodating host for a small number of guests, you would pour the tea for the guest, ask how much sugar the guest wants and add it for them.
Other additives you might serve with tea and which people might or might not add to taste are artificial sweetener (for people who want to watch their calorie intake), lemon juice and milk (depending on the kind of tea).