No, that SDK on GitHub is for Web development only. For desktop development, you need to purchase the desktop SDK. Or as Jay said, don't use an SDK - just use the API which is free for anyone to use. It really depends on what sort of development you want to do.

Dingosoft, thank you for your reply.

We want to be able to integrate the following data flow between Sage and a website.   
1) save into Sage the orders received through the website
2) retrieve inventory, customer information from Sage and display it on website.

For such purposes, do we need to use SDK or not?

Thank you!

Dingosoft, thank you for your reply.

We want to be able to integrate the following data flow between Sage and a website.   
1) save into Sage the orders received through the website
2) retrieve inventory, customer information from Sage and display it on website.

For such purposes, do we need to use SDK or not?

Thank you!

Writing orders from a db to Order Entry can absolutely be accomplished using the API (no SDK required).  
When extracting data for use on your website, you can also use the API, but you may achieve better results reading directly from the database.

To start the process, I'd suggest recording a macro while entering an order.  This will provide a basic framework you should be able to build on.  If you run into specific challenges, there is a wealth of knowledge within the VBA forum for the searching and / or asking.

Thank you Shane!

Is what you said about Sage 300 also applicable to Sage 100?

Thank you!

Hello, to extract data from Sage300, what API we should call?

You don't need an API to do exports, just use SQL queries.  Or select File/Export from a UI.

Have you looked at Realisable IMan?  It's designed for exactly what you appear to be trying to do.  The major, major benefit is that you don't have to learn the API.  It does it for you. 

I always look at Realisable IMan first for this type of project, then move on to API if it's not suitable.  9 times out of 10 Realisable IMan does the job.

for retrieving orders information, what tables we should look at? The tables name don't make sense at all.. any hint?  Thanks Jay!

thank you, will check out

https://support.na.sage.com/selfservice/viewContent.do?externalId=19194&sliceId=1

You want to search in the KB for the object models. That will give you better descriptions of the tables and fields in Sage.

Jay, those links don't work at all.. can you provide another link?

That link is good, I've used it for years, so I don't know what your issue is.  Just google "sage application object module".

When I tried to download the attachments, for example "Sage 300 2019 AOM.zip", nothing happened. 

Yeah, it's broken.  Only Sage can fix it.