Inserting data using JDatabase:

JDatabaseQuery class includes methods such as insert(), columns() and values() to insert data.

For example:

// Get a db connection.
$db = JFactory::getDbo();

// Create a new query object.
$query = $db->getQuery(true);

// Insert columns.
$columns = array('columnn_name_1','column_name_2',......,'column_name_n);

// Insert values.
$values = array($db->quote(value_1),$db->quote('value_2'),.......,value_n); // if value is string then use quote() method to insert else insert it normally without any quote

// Prepare the insert query.
$query
    ->insert($db->quoteName('#__table_name')) //write your table name in place of table_name
    ->columns($db->quoteName($columns))
    ->values(implode(',', $values));

// Set the query using our newly populated query object and execute it.
$db->setQuery($query);
$db->execute();

Updating data using JDatabase:

To update data in database using JDatabaseQuery class two methods are used update() and set().

For example,

// Get a db connection.
$db = JFactory::getDbo();

// Create a new query object.
$query = $db->getQuery(true);

// Fields to update.
$fields = array(
    $db->quoteName('field_name_1') . ' = ' . $db->quote('value1'),
$db->quoteName('field_name_2') . ' = value_2'
);

// Conditions for which records should be updated.
$conditions = array(
    $db->quoteName('field_name') . ' = value'
);

$query->update($db->quoteName('#__tablename'))->set($fields)->where($conditions);

$db->setQuery($query);

$result = $db->execute();

Deleting a record using JDatabase:

Here, delete() method is used to delete the record based on some conditions.

Example:

$db = JFactory::getDbo();

$query = $db->getQuery(true);

// delete record based on value
$conditions = array(
    $db->quoteName('field_name') . ' = value', 

);

$query->delete($db->quoteName('#__table_name'));
$query->where($conditions);

$db->setQuery($query);

$result = $db->execute();