Multiple WHERE Clauses with LINQ extension methods

I have a LINQ query that looks like the following:

DateTime today = DateTime.UtcNow;
var results = from order in context.Orders
              where ((order.OrderDate <= today) && (today <= order.OrderDate))
              select order;

I am trying to learn / understand LINQ. In some cases, I need to add two additional WHERE clauses. In an effort to do this, I'm using:

if (useAdditionalClauses)
{
  results = results.Where(o => o.OrderStatus == OrderStatus.Open)  // Now I'm stuck.
}

As you can see, I know how to add an additional WHERE clause. But how do I add multiple? For instance, I'd like to add

WHERE o.OrderStatus == OrderStatus.Open AND o.CustomerID == customerID

to my previous query. How do I do this using extension methods?

Thank you!