How do i can data from my custom form to a custom table

This is the code to create the form, i have created the table already, it has 3 columns, name [varchar], description [varchar] and date [date]. i am missing the code to include that allows the from to upload the values in the fields to the table please.

<form method = "post" action = "">
<h3>Add a activity</h3>
<p style="font-weight:bold;" label for="supervisor">Supervisor:</label>
<input type="text" name="supervisor"/>
</p>
<p style="font-weight:bold;" label for="description">Description</label>
<input type="text" name="description"/>
</p>
<p style="font-weight:bold;" label for="date">Date</label>
<input id="date" type="date" name="date"/>
</p>
<hr>
<input type="submit" value="Submit" name="activity_submit"/>
</form>
</br>

The table is called wpdb_activity_record ,and image of which is below.

this is the table in the db that i have created