Detailed step of Dijkstra's algorithm performance analysis Reading the book of Dasgupta-Papadimitriou-Vazirani.pdf  about the performance of Dijkstra's algorithm on Page 118, we are given:

4.4.3 Running time
At the level of abstraction of Figure 4.8, Dijkstra's algorithm is structurally identical to breadth-first search. However, it is slower because the priority queue primitives are computationally more demanding than the constant-time eject's and inject's of BFS. Since makequeuetakes at most as long as $|V|$ insert operations, we get a total of $|V|$ deletemin and $|V| + |E|$ insert/decreasekey operations. The time needed for these varies by implementation; for instance, a binary heap gives an overall running time of $O((|V|+|E|)\log |V|)$.

I understand that it has $|V|$ insert and deletemin operations but can someone please explain why we have $|V|+|E|$ insert/decreasekey operations? First of of all, why does one algorithm have TWO kinds of insert operations? If they are the same kind, then where can we learn more about what decreasekey actually does?  The Wikipedia page doesn't seem to cover it much either (unless I missed or misunderstood it).
Since makequeue takes at most as long as $|V|$ insert operations, we get a total of $|V|$ deletemin and $|V | + |E|$ insert/decreasekey operations.
  First of of all, why one algorithm has TWO kinds of insert operations, if they are the same kind, then where can we learn more about what decreasekey actually does?


No, there is only one kind of insert operation. We got 


$|V|$ deletemin operations.
a total of at most $|V|+|E|$ operations, where each operation is either an insert operation or a decreasekey operation. We count these two kinds of operations together because it takes the same asymptotic time to do either one of them, $O(\log |V|)$.  More specifically. we have


|V| insert operations during makequeue.
at most |E| decreasekey operations as each edge may or may not lead to a decreasekey operation.