I installed elementary OS alongside Windows 10, now every time grub menu will show up my PC startup.
Can I enter elementary OS without choosing it? and how can I boot Windows 10 if elementary OS has defaulted?
If you want to dualboot elementary and Windows you'll have to see the grub menu every time you turn your pc on.
However, if you barely use one of those operating systems, you could hide the grub menu and edit a config file every time you want to access the other system. I don't recommend doing this since it's probably not worth the trouble.
To hide your grub menu you need to edit
/etc/default/grub and set the following:
GRUB_DEFAULT="0" GRUB_HIDDEN_TIMEOUT=0.0 GRUB_HIDDEN_TIMEOUT_QUIET=true #GRUB_TIMEOUT=5
You don't need to set any value to
GRUB_TIMEOUT, but you have to add a "#" at the beginning of the line.
IMPORTANT: Check whats the number of the elementary option on the grub menu, if it's the first line (usually yes), then setting
GRUB_DEFAULT="0" will boot that line, otherwise you'd need to change the number.
When you finish editing that file, execute from terminal
sudo update-grub and reboot to see the results.