You can share a post within the Fediverse by selecting the Boost button which is usually spinning arrows, something like this 🔃
You can share posts with people outside the Fediverse by selecting the Share option, which is often shown as an arrow leaving a square.
On Mastodon’s website version, you can also get a direct link to the post by clicking the ⋯ below a post and selecting Copy link to this post. Alternatively, you can get embedding code to put the post on your own blog or website by clicking ⋯ and selecting Embed.