If someone tells you that election turnout doesn't matter,
there are three possible reasons that someone would tell people that:
1. That person doesn't understand how our elections work.
2. That person has lost hope in the system we use to elect people.
3. That person is trying to depress you in hopes you won't vote.
Personally, I don't pay any attention to anyone telling me that turnout doesn't matter. I know that it does. Hillary Clinton lost in the electoral college in the 2016 election over less than 100,000 votes total in three states. More votes than that were cast for third party candidates in those three states. Turnout was down, as well.
Don't pay any attention to anyone telling you that turnout doesn't matter. That's just bullshit. Instead, take two people who wouldn't otherwise vote to the polling place with you. If everyone did that, we'd win in a landslide that couldn't be ignored. Truly.
To hell with ignorance, pessimism, and voter discouragement! Just say no to all three!
Thanks!
= new reply since forum marked as read
It always is. When huge swaths of the populace doesn't vote, the vocal minority parties win.
We need to repeat the 2018 wave. Actually, we need to continue it.
Local offices matter, too. And if someone says they don't know who to vote for, I'm more than willing to explain the issues! 
It's only local races in my district, but I'm glad I looked since I know one of the candidates personally and she's the only Democrat running in a 5 person race. 