make mac bootable pendrive

 first we need to have dmg image of mac

which can be download from mac using the following link

for catalina: catalina

for mojave: mojave

for high sierra: high sierra

for sierra:sierra

for latest direct use mac store to download it

for bootable part

1.  now you need to open terminal and connect usb
2. select image and right click to show image contents
1. click on contents
2. then resources
3. then on createinstallmedia
4. right click on it and get info and copy url 
3. in terminal type sudo <space>  <paste url> <space> --volume <space> /Volumes/<usb name>
1. if usb name has space , then type first name then type \ then second part and so on
4. press enter and press y when prompted
5. in few minutes, the pendrive is ready to boot