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