mjhjmtu

I want to create this table:

I started with this, but it doesn't work:

documentclass[11pt,a4paper]article
usepackage[latin1]inputenc
usepackageamsmath
usepackageamsfonts
usepackageamssymb
usepackagegraphicx
usepackagegraphicx
usepackagesiunitx
usepackagebooktabs
begindocument
begincenter
 begintabularc

 hello & hello \

 toprule
 hello hello hello hello hello hello hello hello hello hello space infinity & hello hello hello hello \
 hello hello hello hello hello & hello hello hello hello \

 endtabular
 endcenter
 enddocument}

How can I fix this?

like this:

beside tabularx are used options !<option> and Xhline<width> from the package array (in this case loaded by the package tabularx) and macro makecell from the package of the same name:

documentclass[11pt,a4paper]article
usepackagemakecell, tabularx

begindocument
begincenter
setcellgapes5ptmakegapedcells
 begintabularxtextwidthX!vline width 1pt X
 makecellhello & makecellhello \
 Xhline1pt
 hello hello hello hello hello hello hello hello hello hello space infinity
 & hello hello hello hello \
 hello hello hello hello hello hello hello hello hello hello space infinity
 & hello hello hello hello \
 endtabularx
 endcenter
enddocument

Don't use booktabs with vertical rules.

And don't load packages twice (you have two usepackagegraphicx).

I have used tabularx, and \[4pt] and rule0pt16pt to add some space before and after the horizontal rule.

documentclass[11pt,a4paper]article
usepackage[latin1]inputenc
usepackagetabularx
begindocument
begincenter
 begintabularxtextwidthX
 multicolumn1chello & 
 multicolumn1chello \[4pt]
 hline
 rule0pt16pthello hello hello hello hello hello hello hello hello hello space infinity & hello hello hello hello \
 hello hello hello hello hello & hello hello hello hello \
 endtabularx
 endcenter
 enddocument

The screenshot that accompanies your query creates the impression that each table column should be just wide enough (but no wider) to typeset three instances of the word "hello", separated by whitespace. If this impression is correct, you should use the p column type for both columns. The p column type takes an argument -- the usable width. In the preamble, be sure to set up a length parameter and measure the width of "hello hello hello" via a settowidth directive.

Oh, and don't use the booktabs package (and midrule directives) if you employ vertical lines. Instead, use hline.

documentclass[11pt,a4paper]article
usepackagearray % for "extrarowheight" macro
newlengthmylen
settowidthmylensffamily hello hello hello % measure width of "hello hello hello"
begindocument
begincenter
sffamily % switch to sans-serif
setlengthextrarowheight2pt % for a more open "look"
begintabularpmylen
multicolumn1chello & 
multicolumn1chello \[2pt]
hline
hello hello hello hello hello hello hello hello hello hello space infinity & hello hello hello hello \
hello hello hello hello hello & hello hello hello hello \
endtabular
endcenter
enddocument