Very basic tutorial.
I want to place phone number between logo and search at the top of the store.
So I go to Views/Shared/Header.cshtml and place between
<div class="header-lower">
<div class="header-logo">
@Html.Action("Logo", "Common")
</div>
<div class="search-box store-search-box">
@Html.Action("SearchBox", "Catalog")
</div>
</div>
New div with resource string. So it would be look like below:
<div class="header-lower">
<div class="header-logo">
@Html.Action("Logo", "Common")
</div>
<div>@T("myspecialphonenumber")</div>
<div class="search-box store-search-box">
@Html.Action("SearchBox", "Catalog")
</div>
</div>
All to do now, is to add new resource string with appropriate value.
So go to Admin panel -> settings -> language, choose your language and in second tab ("String resources") add new record. On resource name should be myspecialphonenumber.
Please note, it is good practice, to made modification only at the Themes view folder, not main. So if you have only Default clean theme, you would need to copy file Header.cshtml from main View folder to /Themes/DefaultClean/Views/Sheared
Hope it would help with first steps :)