Hi, what is the best defense after Scaillin Defense?

I think you might mean the Sicilian Defense. If you are referring to the opening where e4 is responded to with c5, this is the opening. Typically, the best response is to play Nf3 to support the d4 square. After that, oftentimes, you can follow up with d4. If Nf3 is countered with Nc6, you can play Bb5, the Nyezhmetdinov-Rossolimo Attack.

I don't know how to respond but this is useful

I suspect you know move notation, correct? If not, I can tell you how it works.

A good resource on the Scaillin Defense can be found here. Keep in mind that it's generally not recommended to play this opening until you have a rating of around 2000 (or somewhere up of 1500). Considering that you have difficulty winning games around the 100 rating level, you might want to try something simpler.

Hi, you're asking the wrong question. Since your opponent comes up with the defense, you have to think about attacking them.

Keres Attack, English Attack, Polugaevsky, Freak Attack, McDonnell Attack, Myers Attack, Portland Attack, Nyezhmetdinov-Rossolimo, Venice Attack, Velimirovic Attack, Frolov Attack, Amsterdam Attack, Fischer-Sozin Attack, Matanovic Attack, Perenyi Gambit, Grand Prix Attack, Kopec System, Maroczy Bind, Yugoslav Attack, Levenfish Attack, Stockholm Attack (e4-f5-g4 formation), Totsky Attack are all viable strategies to undermine black's defensive position - correct pawn play is essential.

And if that sounds intimidating to you, don't start the Sicilian - yet These are just the known lines.

1. d4

Assuming you mean as Black, against 1. e4...

How to CRUSH with the Caro-Kann! - GothamChess

Note at 9:15 of the video he begins discussion of the Classical Variation (1.e4 c6 2.d4 d5 3.Nc3), which can lead to several sub-variations; in particular, the Korchnoi Variation (aka the Tartakower V., as he refers to it in the video) beginning @10:17 - this is my favorite (dynamic!), variation for Black, when White chooses the Classical Variation (with either 3.Nc3 or 3.Nd2)...

https://www.youtube.com/watch?v=ebfzL_GwiIE

If you are curious about the Korchnoi/Tartakower Variation, here are several instructive introductions to this line.  The first video by Gambit Publications, also serves as an introduction to Sverre Johnsen's book “Win With the Caro-Kann” (GM John Nunn is doing the review), which IMO does an excellent job of teaching this particular variation, and is my first choice as a book to learn it, and the Caro-Kann overall....
https://www.youtube.com/watch?v=6K0zg1b5ETU
https://www.youtube.com/watch?v=-_6qOZIlbE0
https://www.youtube.com/watch?v=J7qKfb_LojU
https://www.youtube.com/watch?v=-MrEYqiMU4w
https://www.youtube.com/watch?v=cPVp5TWZR0w

for comprehensive treatment of the Caro-Kann...

Caro-Kann Defense - Hanging Pawns

https://www.youtube.com/watch?v=Jiz7KLKjLas&list=PLssNbVBYrGcBZfLbeAU7d8llHf2jxBEl7

Caro-Kann Defense - Sibi Chess

https://www.youtube.com/watch?v=6a0S2eTISc4&list=PL-gFa2AFBbmS8kQqrbsiAjr_d6WfpfBZ8&index=30

After the Scaillin Defence I like the French, Caro-Kann and the Petroff. The Scaillin is best though. Especially the Classical Scaillin. I love that one. I sometimes misspell it too.

Eat the pizza