Common interests are actually what start a friendship Friendships actually begin with common interests What makes two people become friends is often shared interest in a topic These are examples of how you could say it. We tend to say "common interests" or "shared interests", rather than "shared topics".

what makes people start a friendship are actually the common topics.

what make people start a friendship that are actually the common topic. i think that!

if i see someone, like you.! hehe.