Poly lines

I have some drawings with polylines I can Delete them, but can not Trim or Lengthen them or Divide them.
Any advice Please.
Paul Meldrew.

Many commands don't work on polylines. Explode them first, they are normal lines then.

Hi, so how does explode work? I click on the object to explode, and it turns into a red dashed line, but how do I OK it? enter doesn't do it, right click doesn't do it, and if I hit cancel, it returns white solid again? there seems to be little logic with this program after being used to Autocad and Draftsight. As an instance, if I want to trim, I click on the line to trim to (OK), then I have to click on the bit I want to keep, instead of the bit I actually want to trim! Illogical!
A very frustrating program so far.

Explode: Select object(s), click on Explode, and done.
 Or evoke Explode first, then select objects by window or one after the other, and close selection by Enter, done.

Trim: Select limiting entity first, then the entity to be trimmed. Ah you have got the procedure right. But it's not illogical, maybe just different understanding of the expression Trim than in Autocad. Trim as to shorten an object, not as the part to be cut off.  

It is, after all, FREE, so you have to get used to it.

Left click on the command EXPLODE.  
Left click (or Window click) to select drawing object(s).  
Right click to ACCEPT.  
Right click and chose EXPLODE (again) from the drop down menu.

Many commands work similarly.  Three (+) decades in AutoCAD here (since before its inception).  There is a learning curve to LibreCAD, trial and error, but progress IS being made - and I LIKE IT, 'cause it's FREE.  The AutoCAD alternative is nearly $3K for an annual license...and THAT is NOT going to happen in retirement.