Once you get the blueprint, you have to go to your inventory and "use" the blueprint to be able to start crafting the item.
Crafting the NRE
Unlike the Condensed Resin, in order to make the NRE, you have to use the blackmsith. There are blacksmiths in all the cities, marked on the map with an anvil icon.
You need 20 Lizard Tails, 20 Chaos Circuits, and 50 Electro Crystals. This is a one time craft, which means that you only need to get enough materials to make it once. It's not a consumable item.
You get Lizard Tails by catching lizards that's out in the world. There is no "designated" place to farm lizards, but they can be found anywhere by destroying bushes. There are plenty of bushes in Starfell Lake area, near the Statue of the Seven - Anemo. Mondstadt also has a lot of bushes too close to the Knights of Favonius' Headquarters.
If some a lizard spawned but you did not manage to catch it before it disappears, you can teleport to a faraway place then teleport to where the lizard was to try and catch it again.
Chaos Circuits are item drops that you get by defeating Ruin Guards and Ruin Hunters. You can find their location by using your Adventurer Handbook, then use the "Bosses" section, and filter the list to "Elite Enemies." Select the Ruin Guard/Hunter, and tap the "Navigate" button.
Electro Crystals can be found mostly in Mondstadt areas, but they are always spread out and far apart from each other. These are the 2 good places to find some Electro Crystals. To "mine" them, you need to attack with a Pyro elemental attack, causing overload and the crystal will drop.
You can find 3 in the area marked in the picture shown above, which is in Liyue region, close to the domain area in Luhua Pool.
Using the NRE
After you finish crafting it, go to your inventory and select the NRE. You can put in 2 different food items so that you can quickly use it in battle without having to go to the menu every time.
You can only put 1 recovery type food, and 1 revival type food. You can't change it to defensive, offensive, or stamina type foods. Select whichever food that you have the most of.
Once you have it equipped, you can see it just above the elemental burst icon. Pressing the designated key will use up the food that you have selected. If any of your party members die, the food will automatically change to the revive food. You won't be able to heal until you revive your fallen party members first, unless the revive food is on cooldown.