Express as the sum or difference of logarithms. \[ \log _{5} 3 y \]

Step 1 ：The given expression is a logarithm of a product. According to the properties of logarithms, the logarithm of a product can be expressed as the sum of the logarithms of the individual factors.

Step 2 ：In this case, the product is 3y, so we can express this as the sum of the logarithms of 3 and y. The base of the logarithm remains the same.

Step 3 ：Using the properties of logarithms, we can rewrite the expression \(\log _{5} 3 y\) as \(\log _{5} 3 + \log _{5} y\).

Step 4 ：Final Answer: \(\boxed{\log _{5} 3 + \log _{5} y}\)