Hi there! "ya que debo trabajar al día siguiente" = "because I have to work the next day". The word "ya" in this context must combine with "que" to mean "because". "Ya que" has the same meaning than "porque". "Siguiente" is an adjective which refers to something later in time, and it normally goes after expressions like "el día", "la mañana", "la semana"...with the meaning "the next". I hope you understand. Regards:)

you put siguiente at the end because if you don't put it. it is not complete, yoiu need to put the time. Other examples are Me voy a dormir temprano, ya que debo trabajar al dìa siguiente. Me voy a dormir temprano, ya que debo ir a trabajar mañana. Espero dormir bien hoy, ya que mañana debo ir a trabajar muy temprano. I hope its exaples help you.