I have been doing this for a while. These are the main ones. There are many that I haven’t listed. Ask, if you need an expertise you don’t see.
SSL certificate purchase and installation (for HTTPS)
Proxy servers for DDOS attacks, caching, optimizing.
Databases (MySQL, MariaDB, Oracle, MSSQL, Paradox, MS Access, and lots more.)
LAMP server administration (LINUX, Apache, MySQL, PHP)
CENTOS, UBUNTU server set-up specialist
Command line administration of most LINUX servers
WordPress, Drupal 7 & 8, Magento 1.9 and 2.x, CMS systems in general
Gmail administration, WHM, CPANEL, Git, VS