Wrzucam do przeglądarki:
http://localhost/spis.html
i dostaję komunikat:
Not Found
The requested URL /spis.html was not found on this server.
Apache/2.4.10 (Debian) Server at localhost Port 80

a ta strona tam jest bo z konsoli:
root@debian:/var/www# ls
spis.html

http://localhost/index.html
też nie działa; jak to naprawić?

To, że w katalogu /var/www masz pliki to jeszcze nie znaczy, że masz tam podpięty vHost. Wrzuć tutaj co masz w pliku/plikach z /etc/apache2/sites-enabled/

jest tylko jeden plik w katalogu

000-default.conf
<VirtualHost *:80>
# The ServerName directive sets the request scheme, hostname and port that
# the server uses to identify itself. This is used when creating
# redirection URLs. In the context of virtual hosts, the ServerName
# specifies what hostname must appear in the request's Host: header to
# match this virtual host. For the default virtual host (this file) this
# value is not decisive as it is used as a last resort host regardless.
# However, you must set it for any further virtual host explicitly.
#ServerName www.example.com

ServerAdmin webmaster@localhost
DocumentRoot /var/www/html

# Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
# error, crit, alert, emerg.
# It is also possible to configure the loglevel for particular
# modules, e.g.
#LogLevel info ssl:warn

ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined

# For most configuration files from conf-available/, which are
# enabled or disabled at a global level, it is possible to
# include a line for only one particular virtual host. For example the
# following line enables the CGI configuration for this host only
# after it has been globally disabled with "a2disconf".
#Include conf-available/serve-cgi-bin.conf
</VirtualHost>

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet

Albo sobie stwórz katalog html w /var/www/ i do niego wrzucaj pliki, albo zamień DocumentRoot na /var/www/ i zrestartuj apache (service apache2 restart)

Dzięki wielkie poszło na dodatkowym katalogu html.