Tomb of Annihilation Help!!

Hello fellow adventurers, 

I have recently started DMing the Tomb of Annihilation book for a party of 5. The party has not yet entered the jungle (we only had 2 sessions, mostly in the starting port)

I have been really struggling to get my head around the mechanics of the hex crawl.

I can't really seem to understand how the pace that the party chooses affects their journey. 

I understand the navigation, the weather mechanic, random encounters and stuff like that. 

However I can't really understand how pace works or even how the hex-crawl works in general.

Sorry if this seems like a bit of a chaotic thread, but would love for some guidance or tips on how to run this in the best way possible!!

I appreciate any feedback and thank you all 

Here's the basic breakdown

Fast: 50% chance to move an extra hex; -5 to Perception checks for avoiding ambushes or finding clues

Normal: Predicatable speed; no benefits or penalties

Slow: 50% chance to move 1 less hex; lets use Stealth while moving so they have a chance to ambush enemies or avoid them entirely

Thank you for that!

I guess I am still a bit confused on the hex-crawl. 

How does the actual jungle exploration work?

Each day, the players choose their intended direction. One of the players, the designated navigator, will make a Survival check (DC 15 in jungle, 10 by the coast/lakes) to see if they move in the right direction. They get a +5 to this check if they are moving slowly, and a -5 if they are moving fast.

If the check is successful, they move where they chose to go.

If they fail, they get lost and move in a random direction chosen by rolling a D6 (one result for each of the 6 adjoining hexes). If they are lost, you do not tell them which hex they end up on. Once they make a successful Survival check (which may take a couple days), you reveal to them where they are on the map.

If the party chooses, they may want to hire a guide from a town or camp to help them navigate, which is sometimes necessary if there is nobody in the party who is decent at making Survival checks.