Three ways to move the cursor, from most reliable to least:
1. Hold down space bar and you'll enter a mode where moving your finger moves the cursor.
2. Drag it from its current location to a new location. This gets finicky, especially if you move your finger out of the text area; the cursor will move to the end of the text, but the highlighted bar that represents where you want to place the cursor will move around on the last line of the text. If there are non-text elements (images, etc.) in the block, then this will be unpredictable in where the cursor ends up. Also your finger blocks the text and there's no more magnifying glass.
3. Single tap in the text to place the cursor -- but if you tap on a misspelled word, it will go into "suggest replacements" mode. Double tap selects a word, and triple tap selects a paragraph.
To select all, you have to have a free cursor (nothing selected) and tap on the cursor itself. To avoid accidentally double-tapping (and thus selecting a word instead of bringing up the context menu) you have to make sure that you wait a beat before tapping again.
To paste (most to least reliable):
1. Do a three finger unpinch gesture, and it will paste at the cursor.
2. Enter the select all menu above and tap on the cursor (same caveats) and one of the options will be paste. But very often the second tap will either activate a double-tap (and thus select a word) or move the cursor a little bit, making a precise paste difficult.