You need 30 points to use wall posts. You can reach 30 points by receiving one up-vote. If you post an accurate and helpful answer, you can easily get a vote. You can check the unanswered list or outdated question list to find questions that need answers.
I think it is unfortunate that wall posts cannot be enabled for people with new accounts, so out of sympathy for you, I have voted your question so you can use wall posts on meta (but not elsewhere, as you don't have 30 points anywhere else). I will unvote the question once you get a vote for real.