Finally I found out how to solve this problem and here the info:
Need to 'modify the file /etc/vhosts/webapp-config and replace vhost_server="apache" by vhost_server="nginx".'
Then I followed https://wiki.gentoo.org/wiki/WordPress in particular the part of creating a database for wordpress by mysql. Here I got only index file of wordpress - so need to this line to /etc/nginx/nginx.conf in order to have GUI interface of wordpress:
'index index.php index.html index.htm;' rather than just 'index index.html;'
Need to 'modify the file /etc/vhosts/webapp-config and replace vhost_server="apache" by vhost_server="nginx".'
Then I followed https://wiki.gentoo.org/wiki/WordPress in particular the part of creating a database for wordpress by mysql. Here I got only index file of wordpress - so need to this line to /etc/nginx/nginx.conf in order to have GUI interface of wordpress:
'index index.php index.html index.htm;' rather than just 'index index.html;'