find searches for files: find /var -name '*.log' finds all log files. grep searches inside files: grep -r 'error' /var/log searches recursively. Combine: find . -name '*.php' | xargs grep 'password'.
Finding Files and Content
# Find files
find / -name "nginx.conf"
find . -name "*.log" -mtime -7 # logs from last 7 days
find . -size +100M # files over 100MB
# Search inside files
grep "error" app.log
grep -r "TODO" src/ # recursive
grep -n "function" app.js # show line numbers
grep -i "error" log.txt # case-insensitive