Question on second stage

I've read the through the first bootsector's code, and everything looks good with objdump: _second_stage_start label is supposed to be at ram 0x7e00 and the code calls it, but I'm trying to make my own second stage and don't understand just how the second stage is placed after the first one. I've tried assembling a program with nasm -f bin and just cat appending to the original file, but that doesn't seem to work, even if the new code is at offset 0x7e00. Am I missing something?

Inizia rileggendo il codice del primo bootsector attorno all’etichetta _second_stage_start e ispeziona il binario con objdump. Riproduci il tentativo riportato con nasm -f bin e la concatenazione, quindi traccia il modo in cui la prima fase individua e carica la seconda fase. Il lavoro è completato quando il repository spiega chiaramente il layout previsto della seconda fase e la procedura di build.