There are 2 cases in Provincial Nominee Programs. Following are they:
1) Firstly, you receive nomination through the province itself, like you have received the nomination from Alberta. So you should accept the Invitation to Apply (ITA) and apply for the visa. You would be issued the Canada PR Visa as per the norms of the said visa. But there is a twist to it. You can't move out of the province with that visa. You have to stay in the province only.
2) Secondly, you get the Invitation to Apply (ITA) from the express entry linked stream of the province. Like what you have mentioned in the latter portion of the question. Under that you'll be straight away picked up by the province from the Express Entry system pool. Moreover, you would receive an extra 600 points, out of 1200, in the Express Entry system as per Comprehensive Ranking System (CRS). This almost guarantees your invitation if you fulfill other criteria as well.
In your case, you fall under the first category. So you need to apply for the
Alberta PNP. You can go ahead. Moreover, as per the latest Express Entry draw, which was held on 12th of June 2019, the score accepted is 465. So, if you want to considered for the express entry system, you need to score the relevant points by compensating in any of the pre-set criteria.
All the best!!