I find the info is bewildering-help!
We're working on making our help and tutorials much easier this year. Plus we're adding videos. But in the meantime I'll be glad to help you with anything that confuses you.
Is there a simple straight forward to setup everything.
Yes. The best place to start is here: Getting started with LimeLM. This tells you how to signup for LimeLM, create a product, and start using TurboActivate (the part of LimeLM you include with your app) in your app.
or how to use the java code
Is your app a Java application? If so read this article: Using TurboActivate with Java
Or are you using another language?
After you've integrated TurboActivate into your app, the you might want to automate the order processing. For that you need a payment processor (PayPal, Authorize.Net, FastSpring, or any of the many many others).
Fastspring seems to be a different company to yours, is it safe to use.
Yes it's safe.
Also is there an alternative to it.
Yes, we list some of them here: http://wyday.com/limelm/help/how-to-generate-product-keys-after-order/