On Mastodon you have 3 different timelines:
HOME - Like Twitter, shows all the posts of the people you follow
LOCAL - Shows all the posts of the members of your Instance
FEDERATED - Shows all the posts of the people that you follow and also the posts of people on other Instances that are followed by people of your Instance
The Instance you choose is very Important and depending on it your experience on Mastodon, the people you will see and the community talk will be very different.
On https://instances.social/ you can easily search instances based on language, interests and some badic policies. The suggestions about Instances on this website are more detailed and precise than the ones on joinmastodon.org