If you do not have a GPU, you can access one of the thousands of GPUs available from cloud service providers including Amazon AWS, Microsoft Azure and IBM SoftLayer. The NVIDIA-maintained CUDA Amazon Machine Image (AMI) on AWS, for example, comes pre-installed with CUDA and is available for use today.
You are now ready to write your first CUDA program. The article, Even Easier Introduction to CUDA, introduces key concepts through simple examples that you can follow along.
The video below walks through an example of how to write an example that adds two vectors.
The Programming Guide in the CUDA Documentation introduces key concepts covered in the video including CUDA programming model, important APIs and performance guidelines.
NVIDIA also provides hands-on training through a collection of self-paced labs. The labs guide you step-by-step through editing and execution of code, and even interaction with visual tools is all woven together into a simple immersive experience.
Practice the techniques you learned in the materials above through more hands-on labs created for intermediate and advanced users.
The CUDA C Best Practices Guide presents established parallelization and optimization techniques and explains programming approaches that can greatly simplify programming GPU-accelerated applications.
For a more formal, instructor-led introduction to CUDA, explore the Introduction to Parallel Programming on UDACITY. The course covers a series of image processing algorithms such as you might find in Photoshop or Instagram. You'll be able to program and run your assignments on high-end GPUs, even if you don't have one yourself.
The CUDA Toolkit is a free download from NVIDIA and is supported on Windows, Mac, and most standard Linux distributions.