I didnt have a hard time with understanding manual flash, the only problem was learning to guess how much power the flash should be (judging by eye). in weddings you dont have time to adjust picture after picture to get the flash right. you need to look at a scene and know, according to the scene and your camera settings what you need. but its very simple really. just time to practice and know what the flash will give.
btw ttl is harder because you need to think what the meter might shoot with how your subject looks. like a white dress or black tux. with manual, you shoot and if the flash hitting them isnt bright or is too dark you can
-keep everything the same and just move in closer or further away, assuming composition for sull body/half body isnt a problem..or
-keep everything the same in camera and dont move but just up/down the power of flash.
manual is very consistent and when you know what the flash power is youre accuarate in every shot. ttl isnt. btw, another thing almost know one knows is that flash and AWB changes the kelvin of the image. thats why I adjust kelvin manually. awb wants to make the image too warm in certain light.
just like I was scared to understand how to manually adjust kelvin. I thought there was a green and red and blue to adjust as well and thought id leave it to auto. but then I realized its just too simple that I laughged after:
-too yellow/warm, lower the number
-too blue/cool raise the number.
and numbers I adjust is between 2500 (indoor with a lot of incandescent light)-5500 (usually late sunset and when im shooting family pictures in the shade)
I now adjust every image manually and its fast and easy and accurate. some venues I shoot have such yellow lighting and the awb would always make it completely yellow. but I now have complete control on making the image look aesthetic.
manual flash is very very easy. a book is more in depth than you need it to be. a person starting out cant absorb so much because he needs to practice those steps and it takes time to see the outcome. so jumping from basic steps to more advanced steps will confuse you. its like me teaching you about getting compression or to shoot me an exaggerated perspective or even selective focus to a specific shot when youre trying to understand about how to shoot a portrait. its too much.
but its very simple. go shoot a doll near a window. get the face at 2/3 side composition towards the light so the short side is lit more. same composition for all images. use a tripod so its consistent each frame so you can compare later. turn flash off. adjust for proper exposure so the doll is exposed like you like. now you want to add a tiny fill flash amount. so turn flash on, shoot. too bright, turn the power down, too little, add more. when I say add/lower, just up/down the amount a bit each time by 1/3 stop. if its really bright or not even showing, then adjust much more.
the harder problem for most is knowing how much to adjust to get the proper shot and in weddings you need to be fast so you cant shoot and adjust tons of times for that 1 shot. I learned from shooting so much how much power the flash needs to be at a certain distance at my set camera speeds. all I do is usually just leave it all the same and adjust myself to the couple. very simple. if I need more or less power, I adjust the flash and shoot.
now there are more variations than this. but the simple basic gist is stay at the composition, too bright, lower the flash power, too little, up the power. another option is not even adjust the flash but get closer or pull back from your subject ,if the composition doesnt matter, for instance, shooting half body or full body. since both are equally good , you can also play with the aperture or shutter or iso but stick with the first step. and btw shutter will not have a direct affect on flash but adding ambient light (what the shutter does) will make the whole picture light up. but this gets more complicated and more things you dont need to deal with now.
start with- simple basic gist is stay at the composition, too bright, lower the flash power, too little, up the power. theres so much more but a basic light properly shot I do is that. set camera and adjust my flash up or down. I get more complex in many other shots but 80% is this.
btw, I love the SB28. wonderful flash. but its a pita to adjust in manual. the buttons are annoying to use. the yongnuo 560III/IV would be perfect for a manual flash if those idiots would have added hss.