Whether or not you can use APIs, JavaScript/CSS customization, and extensions depends on your license plan.
For details on the available license plans, refer to the product website below.
Pricing (Only available in Japanese)

Customer support is available for inquiries regarding API specifications. To send an inquiry, use the e-mail inquiry form. For information on how to contact Customer Support, refer to the following page.
Contacting Customer Support

Customizing kintone via APIs or JavaScript/CSS requires programing knowledge. If you want to develop your own customization, refer to the following websites.

• cybozu developer network (Only available in Japanese)
  This website provides essential information for customization, including API documentation and sample code.
• cybozu developer community (Only available in Japanese)
  This is an online community where users can discuss customization and customization-related issues.

Customization using APIs, JavaScript/CSS, and extensions is dependent on programming. Because of the wide variety of ways to write programs, customer support is not available for inquiries related to customization.

You can also contact partners with requests for customization using APIs, JavaScript/CSS, and extensions. Search for a partner that's right for your operation from Cybozu Partner Network and consult with them. If you're not sure which partner to consult, use the Partner Selection Support Service.

• Cybozu Partner Network (Only available in Japanese)
• Partner Selection Support Service (Only available in Japanese)

Search for the extension that you're looking for on the product website, then contact the provider.
Product website: Extensions (Only available in Japanese)