Joining Multiplayer in Minecraft on a Mac Help

[HowlDash23 79]

I would love to be able to use the multiplayer option on Minecraft because it gets quite lonely after a while playing by myself. Now, I have tired following some of the tutorials I've found online to do this but it seems like every time I try to follow them, either because I'm not that tech savvy or something seems to go wrong, I end up I having to re-download Minecraft all over again. :/  So I'm wondering if anyone could offer any help in what I could do to connect because I have yet to have any luck in trying to figure out this puzzle.