You need a username first. Go to "Create Account" at the top right of the website homepage. Then you just pick a username and password---e-mail is optional.
Go to the search box on the left. For example, if you wanted an article on dog hair (just a random thought...) you type it in the search box.
It will probably say "No page with that title exists."
And it also says, "You can create this page or request it."
Click on "Create" and it'll take you to a blank page and you can start writing the article. But make sure you're logged in first.
or
I suggest you start at the "your first article" help page at http://en.wikipedia.org/wiki/wikipedia:y... which explains what you should know before creating your first Wikipedia article.
There are no general article templates as such, but some individual WikiProjects do suggest a structure. Look at the manual of style at http://en.wikipedia.org/wiki/wp:mos... or see if there is a WikiProject on the topic you want to write about with more specific guidelines. There's a list of them at http://en.wikipedia.org/wiki/wikipedia:w...
To add an image, you upload it at http://en.wikipedia.org/wiki/special:upl... or go to http://commons.wikimedia.org/wiki/... Special:Upload to upload freely licensed images that can then be used on all Wikimedia projects. You add the image to the article by typing [[Image:Name.jpg|thumb|Caption... See the tutorial at http://en.wikipedia.org/wiki/wikipedia:p... for more help.
The search index updates automatically, though not always immediately, so your article will be searchable. The best way to make sure people can find it is to link to it from other articles. You can also add redirects from alternative titles. See http://en.wikipedia.org/wiki/help:redire... for help.
Make sure you search for existing articles on a topic before starting a new page. There are already articles on the topic you mentioned. See http://en.wikipedia.org/wiki/enterprise_... and http://en.wikipedia.org/wiki/human_resou... .
You can't restrict the editing of other people at Wikipedia, except temporarily in cases of severe vandalism.