You have four options, from best to worst (in this order). The first one always works (if automatic insertion is turned on). You can select from the rest.
First, memoQ tries to Insert best TM or corpus hit:
memoQ finds the best match by checking the match rates of all matches for a segment. You can set a minimum match rate in the Minimum match rate spin box. If the best match is below this match rate, memoQ doesn't insert a match from a translation memory or a corpus.
If you are using external translation memories, and you want to include them in the search, check Include TM plugins in search check box. To set up the TM plugins, open Options, and choose TM plugins.
If memoQ could not insert a match from a translation memory or a LiveDocs corpus, it will try to Insert machine translated hit:
Insert machine translated hit if no suitable TM hit is present: Check this check box if you have a machine translation plugin, and you want memoQ to get a machine translation for the segment if there's nothing from the translation memories. If you clear this check box, or you haven't set up machine translation, memoQ skips this step.
To set up machine translation: Open Options, and choose Machine translation.
If machine translation wasn't available, or it was turned off, memoQ tries to Insert fragment assembled hit:
▪Insert assembled hit if no suitable TM hit is present: Check this check box to make memoQ look for a fragment-assembled match that is good enough to be inserted.
A fragment-assembled match is a suggested translation where parts of the source text are replaced by translation memory matches or terms from term bases. Some of the text may still be in the source language.
▪Minimum coverage (% of characters): Set how much of the source text must be translated from fragments. For example, if this is set to 60%, memoQ accepts a fragment-assembled match if it leaves 40% - or less - of the characters in the source language.
Finally, if nothing works, memoQ can Copy source to target:
•Copy source to target if no other match found: Check this check box if want memoQ to copy the source text to the translation if there are no hits. This is turned off by default. If you turn it on, memoQ will always insert something in the target cells after you confirm the previous segment.