how do i find a name and formula for a combination of an anion and a cation?

ex: Na2CO3 + Ba(NO3)2
please help!

Generally, there are three reasons why a reaction will occur.

1. A gas is formed. You need to know those gases. H2, N2, O2, Cl2, plus usual compounds like CO2, CH4, acetylene (C2H2), NO2, and a few others.
2. A precipitate (an insoluble compound) is formed. You need to know the solubility rules for these. Here is a simplified set of those rules. http://www.chem.sc.edu/faculty/morgan/resources/solubility/
3. A slightly ionized substance (a weak electrolyte) is formed (H2O etc).
4. A redox reaction but this is another set of rules.

In this case, BaCO3 is the ppt. Look on the chart and verify that. That tells you a rxn will occur and what the ppt will be. The rest of the equation becomes obvious.
Na2CO3 + Ba(NO3)2 ==> BaCO3 + 2NaNO3