Bronze is a substance you'll probably just need to learn by seeing a lot of it. Both Bronze and Brass look coppery when new.
Bronze forms a patina or corrosion "skin" as it ages. Most metal statues that have a dark blue-green or brownish patina are going to be bronze. Bronze is Copper and Tin, and rather hard and heavy.
Brass is corrosion-resistant, so if it shiny metallic yellow and isn't Gold, it is probably Brass. Brass is Copper and Zinc, rather hard but lighter than Bronze.
Bronze is more commonly used in statues and art objects. Before the discovery of Iron, ancient weapons and tools were made of Bronze (the Bronze age).
Brass is more commonly used for musical instruments like horns, machine parts, cookware, household items.