How do I redirect a user when a button is clicked?

It depends on what you mean by button. If it is a link:

<%= Html.ActionLink("some text", "actionName", "controllerName") %>

For posting you could use a form:

<% using(Html.BeginForm("actionName", "controllerName")) { %>
    <input type="submit" value="Some text" />
<% } %>

And finally if you have a button:

<input type="button" value="Some text" onclick="window.location.href="https://stackoverflow.com/questions/3168577/<%= Url.Action("actionName", "controllerName") %>";" />