Well, to be able to use the Asm( command correctly, you need to know assembly. Unless if you need something really small, then you can just ask for it here (but keep in mind that things in assembly quickly get long and complicated).
A good tutorial to get started is 'Learn ti-83+ assembly in 28 days', which you can easily find on google. To convert small snippets of assembly code to the hexadecimal format, you can use
an instruction set table or the @z80 bot on the #omnimaga irc channel (on the server irc.omnimaga.org, just type @z80 followed by the assembly instructions seperated by \ (example: @z80 ld de, 8 \ add hl, de)).