To search forward, use F6. To search backward, use C-F6.
To search for the same string again, use either F6 or
C-F6 and then press RET without reentering the string.
To search and replace, use F7. Enter the string to search for, press RET, then enter the replacement string and again press RET. This prompt will appear in the minibuffer:
Query replacing STRING1 with STRING2:and the cursor will be placed at the next occurrence of STRING1 waiting for you to press y to replace, n to skip, ! to replace all remaining matches, or q to quit. As usual, pressing ? during the operation will display a menu of available options.