This first part of the story is told entirely through letters between Pamela and her parents.
In this first letter, Pamela informs her parents of the unfortunate death of her mistress. No, not that kind of mistress; here, "mistress" just means the lady Pamela worked for.
Pamela has a couple reasons to be upset about this lady's death. First, she was a good boss, teaching Pamela skills "above [her] degree," such as fancy needlework and writing (4.1).
And then there's the whole employment issue. With Mrs. B dead, Pamela is worried that she'll lose her job and be sent back to her parents.
However, apparently the lady was such a good boss that, even as she was on her deathbed, she was recommending all her servants to her son, taking particular care to mention Pamela by name, crying, "Remember my poor Pamela!" (4.1).
Her son (Mr. B), in turn, respected his mother's wishes and promised to take care of the servants. Really take care of them if you know what we mean.
He promises Pamela the job of attending to his linens, which essentially means she's going to washing his undies. Also, he gave her some cash (four guineas, or about ten dollars) to match the gift of a year's wages that the other members of the staff received.
Being an obedient daughter, Pamela sends the money off to her parents. She's going to have John the Footman deliver the letter and money.
But wait, the letter isn't done—there's a postscript. Pamela says that her former lady's son has just scared the bejeezus out of her by sneaking up asking to look at what she has written.
Pamela was pretty embarrassed and afraid he might be angry (for reasons that are unclear even to her), but she lets him: he's her boss, and apparently reading letters is the same as having access to company email.
Whew. He likes her even better after having read it.
Also, he's all complimentary about Pamela's writing and says that she can keep self-improving by reading his mom's books. (Hope she finds a copy of The Rules on the bookshelf.)
Pamela exclaims some more about her new boss's excellence and signs off.