he best way to answer questions like these it to have some idea about the general ways in which an acid can react with various other types of compounds, and know what is likely to be produce.
An acid such as hydrochloric acid is able to donate a hydrogen ion to something, and also has available a chloride ion. Other acids will have a different anion present, but will react in the same way as HCl.
The chloride ion or any anions in acids can combine with cations, such as the metal ion in a carbonate compound. In this case, the chloride ion will combine with the calcium ion, to make the compound calcium chloride. You will of course, need to use the ionic charges to write the correct formula. Calcium chloride is a salt, and the formula shows a 1:2 ratio in this case.
The hydrogen ion can combine with other anionic things, to make new compounds.
In this case, two hydrogen ions can combine with an oxygen from the calcium carbonate making water. The oxygen can bring with it two electrons from the charge of the carbonate ion.
What is left of the carbonate ion? A carbon atom and two more oxygen atoms, which thus form the compound carbon dioxide.
So the reaction in words is
calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
More generally
An acid + a carbonate (or a hydrogen carbonate) → a salt + water + carbon dioxide
To write it in symbols, it is important to ensure you have the correct formula for everything, and to then balance it correctly. Balancing can be aided by not simply counting atoms, but by noticing overall patterns and looking at where products come from. So the formula of the salt will assist in balancing both the acid and the carbonate on the LHS. After that, the total number of carbonate ions within calcium carbonate will inform you as to how many water molecules you need and how many carbon dioxide molecules you need.
Rather than see every single question as its own task, isolated from everything else, you will do much better to look for patterns in the things you do.