At this point, DLR is still using the "Legacy" FP system. There is no Magic Bands or FP+ at DLR, so you cannot "reserve" your FPs in advance, but for the most part, the FP system at DLR is similar to the FP system that WDW was using
before they went to FP+. You'll insert your ticket into the FP machine to get the FP; they do post the current return time so you'll know if it works for you or not before getting the FP. You can also check the official Disneyland App, which will give you the current return time. Unlike WDW, there is no official grace period (either early or late), so plan on returning during the time window printed on the ticket.
Once you've obtained a FP, you can collect your next FP two hours later
or when the FP window opens, whichever comes first. Let's say it's 9:00 am and you obtained a FP with a return time of 10:15 am to 11:15 am. You'll be able to get your next FP at 10:15 am (when the time window for the most recent FP opens). On the other hand, let's say it's 9:00 am and you obtain a FP with a return time of 2:15 pm to 3:15 pm. You'll be able to get your next FP at 11:00 am (two hours after you pulled your most recent FP).
Caveat #1: There are a handful of "disconnect" FPs. You can obtain these FPs and they do not limit/impact your ability to get another FP immediately. The only "disconnected" attraction FP is for Buzz Lightyear. WoC, Frozen at the Royal Theater (a show), and the A&E M&G (they may no longer be using this) are also "disconnected" FPs. In other words, you could go get a WoC FP and then immediately go get a RSR FP.
Caveat #2: The two parks are "disconnected" from each other. Meaning you can collect a FP in DL and then immediately hop over to DCA and collect a FP there. For example, if you are in DL and pull a FP for Space Mtn, you can immediately go over to DCA (assuming you have park hopper tickets) and get a FP for RSR.
Caveat #3: Once a park ticket has been used to enter a park, you can obtain FPs in either park. So let's say your party all enters DL in the morning. You can then have one person (aka "the runner") hop over to DCA to get FPs in that park. (It's worth noting, I've only ever done this with park hopper tickets, so I don't know if works if someone had a one-park-per-day ticket).
There aren't a huge number of attractions at DLR that use the FP system. Mostly they are the thrill rides and a few of the more popular non-thrill rides. Disneyland.com has a list of the attractions that currently use the FP system:
https://disneyland.disney.go.com/attractions/#/fastpass/
In terms of crowds, it's hard to say what things will be like in February. Traditionally, late-Jan through Feb is among the quieter times in the park, but as noted, crowds seem to be increasing each year and there really isn't any non-busy times anymore. Still, DLR considers February to be non-peak season, so the parks will be operating with shorter hours and reduced entertainment. This year, it appears that they'll be presenting fireworks nightly (which is usual because fireworks are normally only presented Fri to Sun during the non-peak periods). There are some events happening that might impact crowds; I've been tracking what I hear about in the
2016 Calendar of Events and School Breaks thread.
It's worth noting that the Rivers of America (Tom Sawyers Island, Mark Twin, Columbia, Canoes, and Fantasmic!) and the Train will be shutting down in a few days (Jan 10 is the last day) for a lengthy period of time (a year or more) as part of the prep work for Star Wars Land. The Big Thunder Ranch and Jamboree Area is also permanent closing (Big Thunder Railroad - the attraction - is not impacted). Over in DCA, the Aladdin stage show will be dark until the summer as they prep a new Frozen show. Other attractions (e.g., Autopia, Jungle Cruise, and Splash Mountain) may also be down while you are there. DLR doesn't always announce when refurbishments will start or end with much notice.
One other big difference from WDW is dining. DLR opens their dining reservations 60-days in advance (approximately), but dining reservations can usually be obtained with just a few days notice. I still recommend making dining reservations if you know you want eat at a specific restaurant or at a specific time, but it's not critical that you be on-line right when the system rolls (which happens somewhere between midnight and 8:00 am pacific time).
