I need explanation on some digital multimeter (DMM) specifications
What is digital multimeter (DMM) ranges reading; resistance : 400 ohm - 40 Mohm supposed to mean?


It means that the meter has a number of different ranges for measuring resistance, anywhere from 400&Omega; full-scale to 40M&Omega; full-scale.


  would it mean the DMM cannot measure a material resistive property of less than 400 ohm ?


No. The minimum value of resistance that can be displayed depends on the full-scale range and the number of digits in the display. For example, a "4-3/4 digit" meter on the 400&Omega; range would have a resolution of 0.01&Omega;.


  And what does tolerance 1% rdg. indicate which followed by: 5 dgt mean ?


This describes the accuracy of the meter, which is a combination of a couple of factors.


The analog components limit the accuracy to &plusmn;1% of the actual value being measured.
The digital circuitry limits the accuracy to &plusmn;5 counts (i.e., in the least-significant digit of the display) of the actual value.


The overall accuracy will be determined by whichever of these two limits is larger.

For example, if you are measuring a 100&Omega; resistor, the first rule says that the actual value will be between 99&Omega; and 101&Omega;, while the second rule says it is between 99.95&Omega; and 100.05&Omega; &mdash; the first rule applies.

But if you measure a 1&Omega; resistor, the first rule gives 0.99&Omega; - 1.01&Omega; while the second rule gives 0.95&Omega; - 1.05&Omega; &mdash; in this case, the second rule applies.