Tadaa,
now you just need a type of script which handles the input and does whatever you want to do. For example PHP.
This is a form which takes some user input/choice and sends it to the server.
<form method="POST" action="?">
  <label>
    <input name="plan" type="radio" value="1" checked="checked"/> Plan 1 mounth
  </label>
  <br/>
  <label>
    <input name="plan" type="radio" value="3"/> plan 3 mounths
  </label>
  <br/>
  <label>
    <input name="plan" type="radio" value="6"/> plan 6 mounths
  </label>
  <br/><br/>
  <input type="submit" value="go to checkout ">
</form>Edit:
Added values for inputs
6
solved PHP create plan page and after checkout page