Where Do I Begin?
You should begin by doing research. That you’ve made it here is a good first step.
We have a glossary hosted, with plenty of terms that are common things you should know, such as visualization, imposition, wonderland, etc. If anything you read uses a term that confuses you, check out the glossary. It’s under constant scrutiny, so it’s kept very up-to-date.
Also there are a plethora of guides spanning the length of time that we as a community have been researching the phenomenon, each with different ways to approach creation and development of a tulpa. The guides are worth reading, but keep in mind that creating your tulpa is a process that is uniquely yours. Because of that, what you experience might vary from others without it being bad for the creation process. Don’t copy these guides, but learn from them and use them as a help to understand what you could do to help yourself when creating or developing a tulpa.
Ultimately it will involve sitting and thinking, meditating and concentrating on your tulpa, but the approach to these things is something you have complete creative control over. Use the guides as a reference, not as instructions.
There is a rather large section on the website for progress reports as well. These are the journals of creators as they go through the process of creation, imposition and the like, and they chronicle a great many stories that are all good reads. It’s easy to draw inspiration from these stories. If you’re a skeptic, then you might want to give a number of these your attention – you may find some more believable than others, but remember that everyone’s approach and experiences are nigh unique.
Reading through the forums and consulting users on the IRC room #tulpa.info on Rizon are also great ways to find answers for questions or concerns you might have. The IRC in particular is a great place to talk to not only creators and interested folks, but also many tulpas that are present via proxy or possession. It can a bit of a trip to talk to a tulpa about tulpas at the start, but it can also help you understand them better.