Hi, i would like to make a synthesizer.
I have this Nucleo board with STM32H7 chip.
I see there are many more small parts on this board, what is it all ?
Decoupling, core power supply, lots of SMD jumpers for different board configurations, components for whatever external peripherals are on the board, debugging interface, etc. Different Nucleo boards have different complements of peripherals on the board, so you might have different LEDs, switching converter, ethernet, USB OTG, accelerometer, or other things. It depends on which Nucleo board you have, which one is it, specifically? (I don't know what they have for the H7 yet).
I have a plan : solder this board to my experiment board, only the pins on the bottom are not lined up, why ?
Aren't lined up with what? The standard 100mil grid? Because it's not really designed to be soldered into a perf board. It's meant to sit on a bench and get plugged into other things via jumper wires.
Now the question since i dont solder SMD : with all this unused stuff on the board, does it take more energy ?, what is it all for, can i ignore it ?
Some of it will, some of it wont, again, it depends on what's on the board, which depends on which Nucleo you have.
I,m searching for a crystal on the board, i only see small parts, i thought crystals were big sized.
Crystals can be quite small. Not all Nucleo boards have crystals, but they all have footprints for crystals AFAIK. Look for something labeled X1, X2, OSC1, or Y1, those are typical crystal designators. Or look at the schematics/BOM for the board.
Do other persons also solder this whole nucleo board into a project ?, since this board is cheaper then 1 chip.
It's probably not common, personally if I wanted to use a dev board I would want to plug it into a carrier board rather than solder. But using a dev board locks you into whatever peripherals are already there, takes up a bunch of extra space, and limits your choice of MCU, so it's not very common. Sometimes it's done with much more complex "system-on-modules" that package complex applications processors, memory, etc into a module that's designed to be popped into a carrier board (this way the carrier board can be much cheaper in construction than that required to support the complex devices used in the SoM, and you don't have to deal with bringing up a complex architecture, you just plug it in and get Linux or whatever).