How to install dual boot loader ubuntu system with windows

Almost same as below doc:
https://www.ubuntu.com/download/desktop/install-ubuntu-desktop

What you need to do is to act as an advanced user, choose "something else" option in the third step.

We need to allocate space manually.

We need to allocate new partition from free space.
At least two partition is needed.
/

and swap partition.
The size for swap is always 2*memory(I have 4G memory, so I use 8G as my swap size).

That's all we need to differ from the normal installation.
And please select the correct boot loader device like below.

If you can't find ubuntu boot loader option after you completed the installation.
you can check my post and try to fix it.