I have attempted to evoke before with two black candles and a sigil. I don’t even know if the entity was there or maybe an entity was impersonating it.
I never thought candles were necessary or even the sigil to successfully evoke the spirit. Because the doubt doesn’t exist, I can believe more and it work. I can probably do it lying in my bed and just thinking about the entity.
I just need to know if I really am talking to it.
What I have found is that they are items that make it a little easier to evoke, because they entity likes those kinds of candles, or incense. But all in all you really only need your mind and the sigil.
Yes, you can evoke without tools.
However, the tools help put one in the mindset necessary for magick. They are for the magician, not the spirit.
The doubt will only subside through practice, but you will NEVER be 100% sure if you are talking to yourself or a spirit.
We use seals because it is very rare for something other than the spirit connected to the particular seal to appear. When evoking without a seal, you run the risk of having anything that happens to be around and wants to prey on you, pop up and pretend to be something bigger and badder.
Seals = Sigils? Or those are the circles with the name around the sigil? Cheers
I prefer the term “spirit seal” instead of “spirit sigil” simply because it prevents confusion with the Spare style sigils prevalent in Chaos Magick or the sigils designed by the Gallery of Magick in their work.
However, most people use the term sigil for everything.
Would it be better to draw a circle and the name or a picture of the sigil is enough? Recently started bothering me, such a pesky issue 
You don’t need a circle. The circle only serves the purpose of making it easier to focus your gaze on the seal. It’s not mandatory.