There is no ongoing free plan. You start with free credits that last 7 days, no credit card. After that, Team is billed monthly for every active user, with a pooled credit allowance, and you can buy top-ups when it runs low. Direct signups are billed right away; a 7-day seat trial still applies to teammates who join through Slack.
Setup starts by connecting your Google or Microsoft account so Lindy can, in its own words, "run your inbox, prep and take notes on meetings, and handle scheduling." That is your live mailbox and your live calendar, not a copy. If the account belongs to an employer, expect a second obstacle: Google lets Workspace administrators decide which third-party apps may reach Workspace data, so on a locked-down work account the connection can be refused until an admin allows it. Lindy publishes nothing about this either way, so check with whoever runs your email before you plan around it.
Usage is metered in credits (the platform's unit of spend — each thing you make costs some). Lindy's pricing page shows everyday asks costing the fewest credits, research-grade work more, and big builds the most. Credits pool across everyone on the workspace and do not roll over. Run out and, per the same FAQ, "Lindy pauses credit-using actions until your credits reset" — nothing breaks and you are not billed extra.
The documented starting point is Slack, and installing the Lindy app there is normally an administrator's job. There is a web app as well — its sidebar carries Home, Chat, Meetings, Files, Routines, Skills and Integrations — so you are not locked out without Slack, but the quickstart Lindy publishes assumes the Slack route, and how much of a solo setup works without it is not something we could confirm from the public docs.