Voting booths in Israel provide a slip of paper with the party's name. A voter must put the slip into a sealed envelope and insert it into a box. If slips for the party of one's choice are missing, then blank slips and a pen are provided at each voting booth. The voter must write the party letter code on the slip. Write-in ballots for parties not registered are not accepted. There has been accusations of rivals stealing voting slips of other parties in order to thwart people from voting for their choice.
According to the Central Elections Committee, "The voter selects a slip, one slip only, for the list of candidates he/she wishes to vote for, and places it into the envelope. The voter must seal the envelope. One may also use a blank slip, located next to the printed ballots. In such a case, the voter must indicate on the slip, in his/her own writing (in Hebrew or Arabic only) the name and initials of the list for which s/he is casting a vote. Only one ballot may be placed into the envelope. An envelope that contains 2 slips for the same list will not be invalidated though only one vote will be counted. However, an envelope that contains more than 2 identical slips or 2 or more slips from different lists - that entire envelope will be invalidated."
For more information visit the official Central Elections Committee website in English by clicking here: http://www.bechirot.gov.il/elections19/eng/home_eng.aspx