confusion in ruby on rails

I'm new in ruby on rails.Encountered a line

<span id="searchTab" class="<%=yield(:search_tab_id)%>"><%=link_to "Search", search_items_path %></span>

what the line is doing exactly.

I want to implement another tab here named "XYZ" what are the steps I should follow.

what all things I have to add in controllers,views,routes etc