Hi
Check out the following Technical Documents on the Autodesk web site under the Knowledge Base section -
ID: TS22402 - Using the BLOCK command to create a single object from multiple objects
ID: TS22657 - Advantages and disadvantages of using blocks and xrefs
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AutoCAD Online Help File [F1] (hopefully AutoCAD LT is the same) -
Contents tab -> AutoCAD Online Manuals -> User's Guide -> Create and Modify Objects -> Draw Geometric Objects -> Create and Insert Symbols.
Have a good one, Mike