Have you read the tutorials from the beginning?  I'd recommend you do so if you haven't:  It's my goal that the lessons are easy to understand, and thus I can't really explain the difference, you should read about it.

However, I will say that HL is a number, such as a ram location.  (HL) is whatever is stored in RAM at that location.  (HL) can be used almost any place where you can use "One-Byte Register" as a parameter.  If this confuses you, I highly recommend you read from the beginning

I understand the difference between HL and (HL) (i did not read your tutorials from the beginning but i did read Sean Mclaughin's ams in 28 days) my question is what you mean with it. Or better said: what does HL have to do with the commands SRL and SLA? why is it involved. SRA and SLA are on-byte register commands so what does HL have to do with it?
Is (HL) (adress location) modified because you use these commands? or does it destroy HL?

if you are familiar with C or similar languages, think of hl as holding a pointer and (hl) as dereferencing said pointer.  z80 calcs use 2 byte addresses so you need a register pair to hold the address.  The z80 designers probably decided it would be useful if you could directly manipulate the byte pointed to by the address in hl instead of having to load it into one of the registers prior to rotations, shifts, etc.

Note that in almost all cases I can think of, directly manipulating the contents at the address using (hl) as an argument is slower than using a register as an argument.  logical since registers are closer than RAM.  but, it could be useful if you have tied down for registers.

oh this will probably confuse but the ONLY time (hl) does NOT DEREFENCE is

jp (hl)
iirc, this actually tell you to jump to the address that register pair hl holds, or the address that would be stored at (hl) (I forget which, calc84maniac probably knows)

which is why I always thought it was weird that the syntax is
jp (hl)and not
jp hl

it had a rom link? :O

j/k don't worry too much about it

nice

That looks pretty nice

Lesson 15 is now up.  You won't learn to input names yet, because I realized that the lesson was starting to get too long.

Now I'll be doing lesson 17, which teaches you how to draw sprites!  For all you eager beavers, that might come as soon as next week.

Also I sometimes notice references to your tutorials on other forums or IRC when someone asks what's a good ASM tutorial, plus your tutorials are downloaded quite often, so it tells you did an amazing job on them so far.

Dude, thanks for telling me that!  It was definitely my goal to make ASM easy to understand.

Unfortunately, though, the pdf for lesson 4 might not be up for some time.  It's low on my list of priorities