STAGE 3 SPOILER WARNING!
In order to buy the dimensional arts skills you need to collect honey from the Manolia flowers. You are taught how to bloom a Manolia flower by Mina at the start of Stage 3 - The Meadow.
She tells you that whilst playing as the dragon (Efrim) you can exhale using left trigger and this will cause the flowers to bloom. You can recognise a Manolia flower because it is blue, taller than the other flowers and will have small orbs floating upwards around it. There is also usually a butterfly or other creature near it for you to use to regain the wakfu you lose by blooming the flower.
Once they have fully bloomed (the flower will increase in size 3 times before they are fully grown, just keep exhaling until they stop) it will tell you to press A. When you press A you will collect 1 pot of honey.
When you get to the end of a level and it tells you your score there is an option to move your analogue stick to the right. This allows you to access the dimensional arts shop and purchase additional skills. Please note you cannot access this shop whilst in game mode you can only reach it at the end of levels!
Whilst I am sure it is probably possible to gain this achievement throughout a standard play through I would recommend making sure you gain this achievement as early as possible. The shield and the extra stasis pulses in particular makes some of the bosses in the later stages a whole lot easier when playing on the novice level!
Stage 3 is the best place I have found to boost for honey as there are 3 Manolia flowers in the meadow you enter at the very start of the level and only a couple of spiders to kill. After you have bloomed the 3 Manolias you follow an Eliatrope Path up to the next section then Mina explains the next part of the stage to you. This is a save point so you can quit out and then select the level to start again but still keep the 3 pots of honey you have already collected. You can then continue to repeat this until you have enough honey to buy all of the dimensional arts skills then just complete the level to make your purchases!