DCs are used for:
- Transfer of data on the network (eg from sensor to server);
- Transaction (eg sending HNT from one wallet to another);
- Staking (becoming a validator);
- Infrastructure (adding a hotspot, asserting hotspot location) 
- Blockchain routing fees (buying OUI/Subnet blocks)

HNT is used to reward wireless coverage providers.

Demand is driven by all the users of the system. To transfer data across the network for your wireless system (phone, IoT, etc…), you need to use Data Credits, which are created by burning HNT and are non-transferable. To add a Hotspot to the blockchain, you also need to use Data credits.
To become a validator of the system and be able to earn up to 6% of the emitted tokens, you need to stake HNT.

Individuals can purchase a hotspot to be part of a network that provides connectivity to others around them, whether for IoT (eg. sensors for agriculture, smart cities, …) or phone (4G/5G). 
It creates better and cheaper coverage by leveraging individuals instead of relying on centralized Internet Service Providers. 
The more products require connectivity, the more value the protocol has.

HNT tokens are emitted and rewarded to the Hotspots, network validators, and investors. 
Anyone who wants to use the Helium network needs to pay to do so in Data Credits (1 DCs per 24 bytes). The DCs being USD-pegged, this cost doesn’t change over time (1 DC = $0.00001) and needs to be paid based on the device usage, not an annual/monthly fee.

The token economic structure is a Burn-And-Mint Equilibrium.
Security token holders (the team & investors) receive 35% of all mined tokens (ratio decreases with time). The rest of the tokens are distributed to Hotspots (providing coverage/verifying the Network).
HNT are burned (to create Data Credits) to use the network. This creates upward pressure on the price of HNT, which benefits the holders.