To create a poll in Slack without an app, post your question with one emoji next to each option, send it, and add each emoji as a reaction so teammates can vote with one click. That is the only built-in method Slack's help describes; Slack has no native poll command.
For anonymous, recurring or multi-question polls, install a polling app from the Slack Marketplace: Simple Poll adds the /poll command and Polly adds /polly.