tmux copy and paste
Since I always need to search for it, if I need it and not just for scrolling:
[ # start copy mode - Navigate to start of the block to be copied
 # begin selection # end selection/copy ] # paste 
Or if one is in the emacs mode and does not have vi in the EDITOR or VIEWER system variable the inner secquence would be
+ # begin selection - + g # end selection/copy
 
Configuration change
With the following config one can use a more vim like copying
set -g mode-keys vi
unbind p
bind p paste-buffer
bind -t vi-copy 'v' begin-selection
bind -t vi-copy 'y' copy-selection
[ # start copy mode - Navigate to start of the block to be copied
 - v # begin selection
 - y # end selection/copy
 p # paste 
and if one also wants to go into the copy mode without [, but with ESC one should add 
bind Escape copy-mode
to the .tmux.conf
Further reading
Arch Wiki on tmux and a question similar to mine at superuser. And to give some further reedings: A good Cheet cheet on github.