There are ways in which you can manage user's learning curve. It should be noted that a learned user should not feel that the UI is cluttered with information which she no longer needs.
This is a very common recent trend. When user signs up or logs in for the first time, she is shown a help overlay which helps understanding the UI metaphor. The most prominent functions are highlighted on the UI.
Another variant of this approach is to provide a tour for the user. That helps her to understand the process. There are patters regarding how to handle it.
Usually, there is way to restart this from user settings if user has forgotten.
Help icon or dictionary
This slightly old method was ubiquitous on early windows applications where users were shown a ? mark icon at the top right. Users could go on a particular function/button and get more information about it.
Although this no longer is a trend, for enterprise applications where screens are busy and huge data is on screen, such a feature can still prove to be helpful.
It has now matured into an icon next to such a function or a 'Learn More' link. On click of them contextual small information is shown on a small overlay.
There are entire help manuals for applications. This route is primarily taken in case of enterprise applications where there is huge information to be shared along with domain specific information or glossary etc.
For actions where icons are not self explanatory or there is more non standard actions, tooltips can come in handy. You can provide single line information about a function in a tooltip. It has been around since ages and still widely used.
However, you need to study your target users for at least two aspects. The frequency of operation and the learning curve. For example an income tax related website might be accessed once a year and user might need to re-learn the UI. In such case the small in context ? icon can prove to be beneficial. On the other hand, if your users use is frequently, the onboarding UI can be shown initial few times and then can be manually triggered from settings.
The importance should be given on the screen element affordance, the memorability of actions and frequency of use. Then it is easier to select an appropriate method for managing user's learning curve.