You need to do a form submit and then do what you want with the submitted values.
Form template example:
<form method="post"
class="s_website_form"
action="/routing-value"
enctype="multipart/form-data">
<input type="hidden" name="csrf_token" t-att-value="request.csrf_token()"/>
<div style="float: right;">
<!-- html form input fields -->
<select name="group_selection" style="padding: 3px;">
<t t-foreach="selection_options" t-as="option">
<t t-raw="option"/>
</t>
</select>
<button type="submit" class="btn btn-primary">Show</button>
</div>
</form>
Controller example
from odoo import http, _
from odoo.http import request
import odoo.addons.web.controllers.main
@http.route('/routing-value', type='http', auth='user', website=True)
def get_form_values(self, **kwargs):
if request.httprequest.method == 'POST':
selection_value = request.params.get('group_selection')
user_id = http.request.env.context.get('uid')
user = request.env['res.users'].search([('id', '=', user_id)])[0]
# DO STUFF WITH THE GOTTEN DATA
How to get checkbox value: http://learnopenerp.blogspot.com/2018/06/odoo-get-web-form-template-value-in-controller.html
Hope this one helps....