You can get Taiwan Visa in visa Exempt category if you are an Indian and hold a valid US visa. For details view - Taiwan Visa Exempt Entry.
The steps are simple:
1. Go to this website - https://nas.immigration.gov.tw/nase/
2. Select your desired Language and click "Next"
3. Fill up the required details:
a. Pass port details - Number & Expiry date
b. US Visa details - US Visa number (this is the 8 digit number printed in red. It is not the control number) & visa expiry date
4. Other basic details like your date of birth etc.
And you are done. Take a print out and land in Taiwan.
This visa is valid till 1 month after the date of application. What do you do if you want to extend the visa/get visa for some other date? Well you need to be patient and apply for visa one week before expiry as mentioned above and you will get the renewed visa. Please note, if you re nenter details before one week from original expiry date, it will treat it as correction entry and the original expiry date will remain unchanged.