1. Firstly you need to build an instrument as demonstrated in the Building an instrument tutorial.

Next at the bottom of the LFO module select the modulation (+) menu. Select LFOs and then Triangle.

2. Now you have set up an LFO to control the rate of the first LFO. The slider in the middle will dictate how drastic the effect is. If you play with the frequencies of both LFOs you can get some interesting effects. You can also try different waveforms for more combinations and even assign yet another LFO to control the second one :)