Try to join the tables but you can not here the code of the sentence
$consulta = "SELECT * FROM usuario AS u, materiales AS m WHERE ";
$resultado = $conexion->query($consulta) OR DIE("Error al Ejecutar Consulta de Usuario y Materiales".mysqli_error($conexion) );
Image of the User Table
Image of the Table of Materials
I understand that you want a natural product between the table usuario and the table materiales , so I saw in your table users has a column called materials on that column you must do inner join , as follows:
SELECT * FROM usuario INNER JOIN materiales ON usuario.materiales=materiales.idMateriales
If you want to add a condition, just put the where at the end of the sentence above and remember that you must specify on which table you want to do the where for example:
... where usuarios.id=[lo que busques]