Suggestions:
First, you are better off with Dataset[] and Association[] than List[], especially if you have V10.2 or even V10.1. Dataset[] had a steep learning curve but much better tractability and very much better response time.
Second: this will some effort -- maybe a few days or a week's worth considering that you have not done this before.
Your input file is apparently intended for Excel. I'd suggest that you import it into Excel and take another look at it. Your listed column names are: ti tf x y z xdot ydot zdot xsig ysig zsig xdotsig ydotsig zdotsig. There are 14 names, but '2-8=-1=-1_pos.txt' has 16 columns. Suggest using Excel to get the same number to delete some columns, or else add more names to your list. Once you get the columns right, I'd suggest exporting the file as .csv, which is more tractable than a .txt file, just as good practice.
If you lack Excel, try posting again.
Once that is done, you can import the file using SemanticImport[]. I'd suggest some variant on:
SetDirectory[<wherever the file is>.]
symbolName=SemanticImport[<filename>, <| col1name->"Text", col2Name->"Text",col3Name->"Integer", col4Name->"Real", and the rest of the columns Real.|>];
ResetDirectory[];
That should give you a Dataset[] with named columns.
If you want to change symbolName, see Dataset[]. If you want units on the values, see Quantity[].
Once you're that far, try re-posting. If you want to continue on your own, look at guide/MapsAndCartography. Mapping isn't that hard to do once you get your data organized.
Good luck!
